Transmission and reception method and apparatus for reducing transmission time interval in wireless cellular communication system

ABSTRACT

Methods and apparatuses for signal transmission and reception are provided for a wireless communication system. Information for configuring a plurality of physical uplink control channel (PUCCH) resources is transmitted to a terminal. Downlink control information (DCI) is transmitted to the terminal on a physical downlink control channel (PDCCH). The DCI includes a resource indicator for indicating a PUCCH resource among the plurality of PUCCH resources. Uplink control information (UCI) is received from the terminal on the PUCCH resource indicated by the resource indicator.

PRIORITY

This application is a Continuation application of U.S. application Ser.No. 17/077,523, filed in the U.S. Patent and Trademark Office (USPTO) onOct. 22, 2020, which is a Continuation application of U.S. applicationSer. No. 16/437,959, filed in the USPTO on Jun. 11, 2019, now U.S. Pat.No. 11,395,293, issued on Jul. 19, 2022, which is a Continuationapplication of U.S. patent application Ser. No. 15/562,343, filed at theUSPTO on Sep. 27, 2017, now U.S. Pat. No. 10,595,312, issued on Mar. 17,2020, which is a National Phase Entry of PCT International ApplicationNo. PCT/KR2016/003441, filed on Apr. 4, 2016, which claims priority toKorean Patent Application No. 10-2015-0046828, filed on Apr. 2, 2015,and Korean Patent Application No. 10-2015-0102675, filed on Jul. 20,2015, the contents of each of which are incorporated herein byreference.

BACKGROUND 1. Field

The present invention relates to a wireless communication system and,more particularly, to a method and apparatus for data transmission andreception with a reduced transmission time interval.

2. Description of Related Art

To cope with the increasing demand for wireless data traffic aftercommercialization of 4G communication systems, active efforts areunderway to develop enhanced 5G or pre-5G communication systems. Assuch, 5G or pre-5G communication systems are referred to as beyond 4Gcommunication systems or post LTE systems.

To achieve high data rates, use of the extremely high frequency (mmWave)band (e.g. 60 GHz band) is expected in a 5G communication system. Toreduce propagation pathloss and to increase propagation distance at themmWave band, use of various technologies such as beamforming, massiveMIMO, full dimensional MIMO (FD-MIMO), array antenna, analog beamformingand large scale antenna are under discussion for 5G communicationsystems.

To enhance system networks, various technologies such as evolved oradvanced small cell, cloud radio access network (cloud RAN), ultra-densenetwork, device-to-device (D2D) communication, wireless backhaul, movingnetwork, cooperative communication, Coordinated Multi-Points (CoMP) andinterference cancellation are under development for 5G communicationsystems.

In addition, for 5G communication systems, hybrid FSK and QAM modulation(FQAM) and sliding window superposition coding (SWSC) are underdevelopment for advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse codemultiple access (SCMA) are under development for advanced access.

In the LTE system as a representative example of a wideband wirelesscommunication system, Orthogonal Frequency Division Multiplexing (OFDM)is used for the downlink (DL) and Single Carrier Frequency DivisionMultiple Access (SC-FDMA) is used for the uplink (UL). The uplink refersto a radio link through which a user equipment (UE) or mobile station(MS) sends a data or control signal to a base station (BS or eNode B),and the downlink refers to a radio link through which a base stationsends a data or control signal to a user equipment. In such multipleaccess schemes, time-frequency resources used to carry user data orcontrol information are allocated so as not to overlap each other (i.e.maintain orthogonality) to thereby identify the data or controlinformation of a specific user.

The LTE system employs Hybrid Automatic Repeat reQuest (HARQ) toretransmit data at the physical layer when a decoding error has occurredin the initial transmission. HARQ is a scheme that enables the receiverhaving failed in decoding data to transmit information (NACK) indicatingthe decoding failure to the transmitter so that the transmitter canretransmit the corresponding data at the physical layer. The receivermay combine the retransmitted data with the previously received data forwhich decoding has failed, increasing data reception performance. Whenthe data is correctly decoded, the receiver may send information (ACK)indicating successful decoding to the transmitter so that thetransmitter can transmit new data.

FIG. 1 illustrates a basic structure of the time-frequency domain in thedownlink of the LTE system serving as radio resources for transmittingdata or control channels.

In FIG. 1 , the horizontal axis denotes the time domain and the verticalaxis denotes the frequency domain. In the time domain, the minimum unitfor transmission is OFDMA symbols, N_(symb) OFDMA symbols 102 constituteone slot 106, and two slots constitute one subframe 105. The length of aslot is 0.5 ms and the length of a subframe is 1.0 ms. The radio frame114 is a time domain unit composed of 10 subframes. In the frequencydomain, the minimum unit for transmission is subcarriers, and the totalsystem bandwidth is composed of total N_(BW) subcarriers 104.

The basic unit of resources in the time-frequency domain is a resourceelement (RE) 112. The RE may be represented by an OFDM symbol index anda subcarrier index. A resource block (RB, or physical resource block(PRB)) 108 is defined by N_(symb) consecutive OFDM symbols 102 in thetime domain and N_(RB) consecutive subcarriers 110 in the frequencydomain. Hence, one RB 108 is composed of N_(symb)×N_(RB) REs 112. Ingeneral, the minimum unit for data transmission is a resource block.Normally, in the LTE system, N_(symb) is set to 7 and N_(RB) is set to12, and N_(BW) and N_(RB) are proportional to the system transmissionbandwidth. The data rate may increase in proportion to the number ofresource blocks scheduled for the user equipment. The LTE system definesand operates six transmission bandwidths. In the case of an FDD systemwhere downlink and uplink frequencies are separately used, the downlinktransmission bandwidth may differ from the uplink transmissionbandwidth. The channel bandwidth denotes an RF bandwidth correspondingto the system transmission bandwidth. Table 1 illustrates acorrespondence between the system transmission bandwidth and the channelbandwidth defined in the LTE system. For example, the transmissionbandwidth of an LTE system having a channel bandwidth of 10 MHz iscomposed of 50 resource blocks.

TABLE 1 Channel bandwidth 1.4 3 5 10 15 20 BW_(Channel)[MHz]Transmission bandwidth 6 15 25 50 75 100 configuration N_(RB)

In a subframe, N initial OFDM symbols are used to transmit downlinkcontrol information. In general, N={1, 2, 3}. The value of N varies foreach subframe according to the amount of control information to be sentat the current subframe. The control information may include a controlchannel transmission interval indicator indicating the number of OFDMsymbols carrying control information, scheduling information fordownlink data or uplink data, and HARQ ACK/NACK signals.

In the LTE system, scheduling information for downlink data or uplinkdata is sent by the base station to the UE in the form of DownlinkControl Information (DCI). Various DCI formats are defined. The DCIformat to be used may be determined according to various parametersrelated to scheduling information for uplink data (UL grant), schedulinginformation for downlink data (DL grant), compact DCI with a small size,spatial multiplexing using multiple antennas, and power control DCI. Forexample, DCI format 1 for scheduling information of downlink data (DLgrant) is configured to include at least the following pieces of controlinformation.

-   -   Resource allocation type 0/1 flag: this indicates whether the        resource allocation scheme is of type 0 or type 1. Type 0        indicates resource allocation in the unit of Resource Block        Group (RBG) by use of a bitmap. In the LTE system, the basic        scheduling unit is a resource block (RB) represented as a        time-frequency domain resource. An RBG including multiple RBs is        the basic scheduling unit for type 0. Type 1 indicates        allocation of a specific RB in one RBG.    -   Resource block assignment: this indicates an RB allocated for        data transmission. The resource represented by resource block        assignment is determined according to the system bandwidth and        resource allocation scheme.    -   Modulation and coding scheme (MCS): this indicates the        modulation scheme applied for data transmission and the        transport block size for data to be sent.    -   HARQ process number, this indicates the process number of the        corresponding HARQ process.    -   New data indicator: this indicates either initial transmission        for HARQ or retransmission.    -   Redundancy version: this indicates the redundancy version for        HARQ.    -   TPC (Transmit Power Control) command for PUCCH: this indicates a        TPC command for Physical Uplink Control Channel (PUCCH) being an        uplink control channel.

DCI is channel coded, modulated, and sent through Physical DownlinkControl Channel (PDCCH or control information) or EPDCCH (enhanced PDCCHor enhanced control information).

In general, for each UE, DCI is scrambled with a specific Radio NetworkTemporary Identifier (RNTI, or UE ID), appended by a cyclic redundancycheck (CRC) value, channel coded, and transmitted via independent PDCCH.In the time domain, PDCCH is mapped and transmitted during the controlchannel transmission interval. In the frequency domain, the mappingposition of PDCCH is determined by the identifier (ID) of each UE andPDCCH is dispersed across the overall system transmission bandwidth.

Downlink data is sent via Physical Downlink Shared Channel (PDSCH)serving as a physical downlink data channel. The PDSCH is sent after thecontrol channel transmission interval. Scheduling information for PDSCHsuch as mapping positions in the frequency domain or the modulationscheme is notified by DCI transmitted on the PDCCH.

The base station uses the 5-bit MCS field of control informationconstituting DCI to notify the UE of the modulation scheme applied toPDSCH (to be sent to UE) and the size of data to be sent (transportblock size (TBS)). TBS indicates the size of a transport block (TB)before channel coding is applied for error correction.

Modulation schemes supported by the LTE system include QPSK (QuadraturePhase Shift Keying), 16QAM (Quadrature Amplitude Modulation), and 64QAM,whose modulation order (Q_(m)) is 2, 4 and 6, respectively. That is, itis possible to send 2, 4, and 6 bits per symbol by using QPSK, 16QAM,and 64QAM, respectively.

FIG. 2 is an illustration of a time-frequency domain structure of PUCCHtransmission in the LTE-A system according to a related art. In otherwords, FIG. 2 illustrates a time-frequency domain structure of PUCCHtransmission in the LTE-A system where PUCCH (Physical Uplink ControlChannel) is a physical layer control channel through which the UE sendsUplink Control Information (UCI) to the base station.

The UCI may include at least one of the following pieces of controlinformation.

-   -   HARQ-ACK: when no error is found in downlink data received from        the base station through Physical Downlink Shared Channel        (PDSCH, serving as a downlink data channel) to which HARQ is        applied, the UE feedbacks ACK (Acknowledgement); and when an        error is found therein, the UE feedbacks NACK (Negative        Acknowledgement).    -   Channel Status Information (CSI): this includes Channel Quality        Indicator (CQI), Precoding Matrix Indicator (PMI), Rank        Indicator (RI), and signal carrying downlink channel        coefficients. To achieve a desired level of data reception        performance, the BS may set the Modulation and Coding Scheme        (MCS) for data to be sent to the UE to a suitable value on the        basis of CSI information obtained from the UE. The CQI indicates        the signal to interference and noise ratio (SINR) for the full        system bandwidth (wideband) or a part thereof (subband) and is        normally represented as an MCS value indicating a specific level        of data reception performance. The PMI/RI indicates precoding        and rank information needed by the BS to send data through        multiple antennas in a system supporting Multiple Input Multiple        Output (MIMO). The signal carrying downlink channel coefficients        may provide more detailed channel status information compared        with the CSI signal, but with increased uplink overhead. Here,        the UE is notified in advance, through higher layer signaling,        by the BS of CSI configuration information, such as reporting        mode indicating specific information items to be fed back,        resource information indicating resources to be used, and        transmission period. The UE sends CSI information to the BS by        use of the CSI configuration information received in advance.

In FIG. 2 , the horizontal axis denotes the time domain and the verticalaxis denotes the frequency domain. In the time domain, the minimum unitfor transmission is SC-FDMA symbols 201, N_(symb) ^(UL) SC-FDMA symbolsconstitute one slot 203 or 205, and two slots constitute one subframe207. In the frequency domain, the minimum unit for transmission issubcarriers, and the total system transmission bandwidth 209 is composedof total N_(BW) subcarriers. The value of N_(BW) is proportional to thesystem transmission bandwidth.

The basic unit of resources in the time-frequency domain is a resourceelement (RE). The RE may be represented by an SC-FDMA symbol index and asubcarrier index. A resource block (RB) 211 or 217 is defined byN_(symb) ^(UL) consecutive SC-FDMA symbols in the time domain and N_(sc)^(RB) consecutive subcarriers in the frequency domain. Hence, one RB iscomposed of N_(symb) ^(UL)×N_(sc) ^(RB) REs. In general, the minimumunit for transmitting data or control information is a resource block.The PUCCH is mapped to one RB in the frequency domain and transmittedfor one subframe.

FIG. 2 illustrates a case where N_(symb) ^(UL)=7, N_(sc) ^(RB)=12, andN_(RS) ^(PUCCH)=2 (the number of reference signals in one slot forchannel estimation). Reference signals (RS) use constant amplitude zeroauto-correlation (CAZAC) sequences. CAZAC sequences have a constantamplitude and have an autocorrelation of zero. When a given CAZACsequence is cyclically shifted (CS) by a value greater than the delayspread of the propagation path to produce a new CAZAC sequence, theoriginal CAZAC sequence and the new CAZAC sequence are orthogonal.Hence, a CAZAC sequence of length L may be used to generate up to Lcyclically-shifted orthogonal CAZAC sequences. The length of a CAZACsequence applied to the PUCCH is 12 (the number of subcarriersconstituting one RB).

The UCI is mapped to a SC-FDMA symbol to which an RS is not mapped. FIG.2 shows a case where total 10 UCI modulation symbols d(0), d(1), . . . ,d(9) (213 and 215) are mapped respectively to SC-FDMA symbols in onesubframe. To multiplex UCI information of different UEs, each UCImodulation symbol is multiplied by a CAZAC sequence cyclically-shiftedby a given value and mapped to the corresponding SC-FDMA symbol. Toachieve frequency diversity, frequency hopping is applied to the PUCCHon a slot basis. The PUCCH is placed at an outer portion of the systemtransmission bandwidth so that the remaining portion thereof may be usedfor data transmission. For example, in the first slot of a subframe, thePUCCH is mapped to RB 211 disposed at an outermost portion of the systemtransmission bandwidth. In the second slot, the PUCCH is mapped to RB217 disposed at another outermost portion of the system transmissionbandwidth, where the frequency for RB 217 is different from that for RB211. In general, the positions of the RBs to which the PUCCH for sendingHARQ-ACK information and the PUCCH for sending CSI information aremapped do not overlap each other.

In the LTE system, for the PDSCH (physical layer channel for downlinkdata transmission) or the PDCCH/EPDDCH containing semi-persistentscheduling (SPS) release, the timing of the PUCCH or PUSCH (uplinkphysical layer channel sending HARQ ACK/NACK) may be fixed. For example,in the LTE system operating in frequency division duplex (FDD) mode, forthe PDSCH or PDCCH/EPDCCH containing SPS release transmitted at n−4^(th)subframe, HARQ ACK/NACK is sent through the PUCCH or PUSCH at n^(th)subframe.

The LTE system adopts an asynchronous HARQ scheme where the dataretransmission timing is not fixed in the downlink. That is, when HARQNACK is fed back by the UE in response to initial data transmission fromthe BS, the BS may determine the retransmission timing freely accordingto the scheduling operation. For HARQ operation, the UE buffers the datacausing a decoding error and combines the buffered data with the nextretransmission data.

The LTE system adopts a synchronous HARQ scheme having fixed datatransmission points in the uplink unlike downlink HARQ. That is, theuplink/downlink timing relationship among Physical Uplink Shared Channel(PUSCH), Physical Downlink Control Channel (PDCCH) followed by thePUSCH, and Physical Hybrid Indicator Channel (PHICH) carrying downlinkHARQ ACK/NACK corresponding to the PUSCH are fixed according to thefollowing rules.

If the PDCCH carrying uplink scheduling control information or the PHICHcarrying downlink HARQ ACK/NACK is received from the BS at n^(th)subframe, the UE transmits the PUSCH carrying uplink data correspondingto the control information at n+k^(th) subframe. Here, k is specifieddifferently for the FDD or TDD (time division duplex) mode and itsconfigurations. For example, k is fixed to 4 for the FDD LTE system.

If the PHICH carrying downlink HARQ ACK/NACK is received from the BS ati^(th) subframe, the PHICH corresponds to the PUSCH having beentransmitted by the UE at i-k^(th) subframe. Here, k is specifieddifferently for the FDD or TDD mode and its configurations. For example,k is fixed to 4 for the FDD LTE system.

For a cellular wireless communication system, one of importantperformance criteria is the latency of packet data. To this end, in theLTE system, signals are sent and received on a subframe basis with atransmission time interval (TTI) of 1 ms. The LTE system may support UEswith a shortened-TTI less than 1 ms (shortened-TTI UE or shorter-TTIUE). Shortened-TTI UEs can be suitable for latency-critical servicessuch as Voice over LTE (VoLTE) and remote control services.Shortened-TTI UEs can also be used to realize cellular-based missioncritical Internet of Things (IoT).

In the current LTE or LTE-A system, base stations and user equipmentsare designed to transmit and receive on a subframe basis with a 1 msTTI. To support a shortened-TTI UE with a TTI less than 1 ms in anenvironment where regular BSs and UEs operate with a 1 ms TTI, it isnecessary to specify transmission and reception operations differentfrom those of a regular LTE or LTE-A UE. Accordingly, the presentinvention proposes a detailed scheme that enables a regular LTE or LTE-AUE and a shortened-TTI UE to operate together in the same system.

Hence, in the LTE or LTE-A system supporting a short transmission timeinterval (TTI), it is necessary to define, for each TTI, downlinkphysical channels including Physical Downlink Control Channel (PDCCH),Enhanced Physical Downlink Control Channel (EPDCCH), Physical DownlinkShared Channel (PDSCH), Physical Hybrid ARQ Indicator Channel (PHICH)and Physical Control Format Indicator Channel (PCFICH), uplink physicalchannels including Physical Uplink Control Channel (PUCCH) and PhysicalUplink Shared Channel (PUSCH), and a HARQ transmission scheme for thedownlink and the uplink.

SUMMARY

To solve the above problems, an aspect of the present invention is todefine the PDCCH, EPDCCH, PDSCH, PHICH, PCFICH, PUCCH and PUSCH for eachTTI in the LTE or LTE-A system supporting a TTI less than 1 ms. Anotheraspect of the present invention is to define a HARQ transmission methodfor the downlink and the uplink in the above system. Another aspect ofthe present invention is to provide a resource allocation method andapparatus for the above physical channels and HARQ transmission.

In accordance with an aspect of the present invention, a methodperformed by a base station in a wireless communication system isprovided. Information for configuring a plurality of PUCCH resources istransmitted to a terminal. DCI is transmitted to the terminal on aPDCCH. The DCI includes a resource indicator for indicating a PUCCHresource among the plurality of PUCCH resources. UCI is received fromthe terminal on the PUCCH resource indicated by the resource indicator.

In accordance with another aspect of the present invention, a methodperformed by a terminal in a wireless communication system is provided.Information for configuring PUCCH resources is received from a basestation. DCI is received from the base station on a PDCCH. The DCIincludes a resource indicator for indicating a PUCCH resource among theplurality of PUCCH resources. UCI is transmitted to the base station onthe PUCCH resource indicated by the resource indicator.

In accordance with another aspect of the present invention, a basestation is provided in a wireless communication system. The base stationincludes a transceiver and a controller coupled with the transceiver.The controller is configured to transmit, to a terminal, information forconfiguring a plurality of PUCCH resources. The controller is alsoconfigured to transmit, to the terminal, DCI on a PDCCH. The DCIincludes a resource indicator for indicating a PUCCH resource among theplurality of PUCCH resources. The controller is further configured toreceive, from the terminal, UCI on the PUCCH resource indicated by theresource indicator.

In accordance with another aspect of the present invention, a terminalis provided in a wireless communication system. The terminal includes atransceiver and a controller coupled with the transceiver. Thecontroller is configured to receive, from a base station, informationfor configuring a plurality of PUCCH resources. The controller is alsoconfigured to receive, from the base station, DCI on a PDCCH. The DCIincludes a resource indicator for indicating a PUCCH resource among theplurality of PUCCH resources. The controller is further configured totransmit, to the base station, UCI on the PUCCH resource indicated bythe resource indicator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a time-frequency domain structure for downlinktransmission in the LTE or LTE-A system according to a related art.

FIG. 2 illustrates a time-frequency domain structure for uplinktransmission in the LTE or LTE-A system according to a related art.

FIG. 3A illustrates the structure of a radio resource regioncorresponding to one subframe and one PRB through which data or controlchannels are transmitted in the downlink of the LTE or LTE-A systemaccording to a related art.

FIG. 3B depicts a base station procedure carried out when the BSreceives UE capability information on capabilities supported by the UEfrom the UE.

FIG. 3C depicts a procedure used by the UE to send UE capabilityinformation to the BS.

FIG. 4 depicts a BS procedure according to the first embodiment of thepresent invention.

FIG. 5 depicts a UE procedure according to the first embodiment of thepresent invention.

FIG. 6 depicts a BS procedure according to the second embodiment of thepresent invention.

FIG. 7 depicts a UE procedure according to the second embodiment of thepresent invention.

FIG. 8 depicts a BS procedure according to the third embodiment of thepresent invention.

FIG. 9 depicts a UE procedure according to the third embodiment of thepresent invention.

FIG. 10 depicts a BS procedure according to the fourth embodiment of thepresent invention.

FIG. 11 depicts a UE procedure according to the fourth embodiment of thepresent invention.

FIG. 12 depicts a BS procedure according to the fifth embodiment of thepresent invention.

FIG. 13 illustrates regions to which downlink control resources for theshortened-TTI UE can be mapped according to the fifth embodiment of thepresent invention.

FIG. 14 illustrates regions to which downlink control resources for theshortened-TTI UE can be mapped according to the fifth embodiment of thepresent invention.

FIG. 15 illustrates regions to which downlink control resources for theshortened-TTI UE can be mapped according to the fifth embodiment of thepresent invention.

FIG. 16 depicts a UE procedure according to the fifth embodiment of thepresent invention.

FIG. 17 depicts a BS procedure according to the sixth embodiment of thepresent invention.

FIG. 18 depicts a UE procedure according to the sixth embodiment of thepresent invention.

FIG. 19 depicts a BS procedure according to the seventh embodiment ofthe present invention.

FIG. 20 illustrates a region in which the PDSCH is mapped to an entiresubframe for the shortened-TTI UE according to the 6.5^(th) embodimentof the present invention.

FIG. 21 depicts a BS procedure according to the 6.5^(th) embodiment ofthe present invention.

FIG. 22 depicts a UE procedure according to the 6.5^(th) embodiment ofthe present invention.

FIG. 23 depicts a UE procedure according to the seventh embodiment ofthe present invention.

FIG. 24 depicts a BS procedure according to the eighth embodiment of thepresent invention.

FIG. 25 illustrates shortened-TTI PUCCH transmission according to theeighth embodiment of the present invention.

FIG. 26 illustrates shortened-TTI PUCCH transmission according to theeighth embodiment of the present invention.

FIG. 27 illustrates shortened-TTI PUCCH transmission according to theeighth embodiment of the present invention.

FIG. 28 illustrates shortened-TTI PUCCH resource mapping according tothe eighth embodiment of the present invention.

FIG. 29 illustrates shortened-TTI PUCCH resource mapping according tothe eighth embodiment of the present invention.

FIG. 30 illustrates shortened-TTI PUCCH resource mapping according tothe eighth embodiment of the present invention.

FIG. 31 depicts a UE procedure according to the eighth embodiment of thepresent invention.

FIG. 32 depicts a BS procedure according to the ninth embodiment of thepresent invention.

FIG. 33 depicts a UE procedure according to the ninth embodiment of thepresent invention.

FIG. 34 depicts a BS procedure according to the tenth embodiment of thepresent invention.

FIG. 35 depicts a UE procedure according to the tenth embodiment of thepresent invention.

FIG. 36 depicts a BS procedure according to the eleventh embodiment ofthe present invention.

FIG. 37 depicts another BS procedure according to the eleventhembodiment of the present invention.

FIG. 38 shows a user equipment including a receiver, processor andtransmitter employed in various embodiments of the present invention.

FIG. 39 shows a base station including a receiver, processor andtransmitter employed in various embodiments of the present invention.

FIG. 40 depicts a BS procedure according to the twelfth embodiment ofthe present invention.

FIG. 41 depicts a UE procedure according to the twelfth embodiment ofthe present invention.

FIG. 42 illustrates the structure of downlink control and data signalsaccording to the thirteenth embodiment of the present invention.

FIG. 43 illustrates the structure of downlink control and data signalsaccording to the thirteenth embodiment of the present invention.

FIG. 44 shows a table that specifies the points in time when the UEsends a HARQ ACK/NACK signal to the BS according to the fourteenthembodiment of the present invention.

FIGS. 45A, 45B, 45C, 45D, and 45E show tables that specify the points intime when the UE sends a HARQ ACK/NACK signal to the BS according to thefourteenth embodiment of the present invention.

FIGS. 46A, 46B, 46C, 46D, and 46E show tables that specify the points intime when the UE sends a HARQ ACK/NACK signal to the BS according to thefourteenth embodiment of the present invention.

FIG. 47 depicts a UE procedure according to the fourteenth embodiment ofthe present invention.

FIG. 48 shows a table that specifies the points in time when the BSsends a HARQ ACK/NACK signal to the UE according to the fifteenthembodiment of the present invention.

FIGS. 49A, 49B, 49C, 49D, and 49E show tables that specify the points intime when the BS sends a HARQ ACK/NACK signal to the UE according to thefifteenth embodiment of the present invention.

FIGS. 50A, 50B, 50C, 50D, and 50E show tables that specify the points intime when the BS sends a HARQ ACK/NACK signal to the UE according to thefifteenth embodiment of the present invention.

FIG. 51 depicts a BS procedure according to the fifteenth embodiment ofthe present invention.

FIG. 52 shows a table used for determining the TBS index based on theMCS index in the existing LTE system.

FIGS. 53A and 53B show tables used for determining the TBS according tothe TBS index and the number of allocated PRBs in the existing LTEsystem.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention are described indetail with reference to the accompanying drawings. Detaileddescriptions of well-known functions and structures incorporated hereinmay be omitted to avoid obscuring the subject matter of the presentinvention. Particular terms may be defined to describe the presentinvention in the best manner. Accordingly, the meaning of specific termsor words used in the specification and the claims should be construed inaccordance with the spirit of the present invention. In the followingdescription, the term “base station” is a main agent allocatingresources to UEs and may refer to at least one of eNode B, Node B, BS,radio access unit, base station controller, and network node. The term“user equipment (UE)” may refer to at least one of mobile station (MS),cellular phone, smartphone, computer, and multimedia system with acommunication function. The term “downlink (DL)” refers to a wirelesstransmission path through which the BS sends a signal to the UE, and theterm “uplink (UL)” refers to a wireless transmission path through whichthe UE sends a signal to the BS. The following description ofembodiments is focused on the LTE or LTE-A system. However, it should beunderstood by those skilled in the art that the subject matter of thepresent invention is applicable to other communication systems havingsimilar technical backgrounds and channel configurations withoutsignificant modifications departing from the scope of the presentinvention.

In the following description, a shortened-TTI UE may be referred to as afirst type UE, and a normal-TTI UE may be referred to as a second typeUE. The first type UE may refer to a UE that can transmit controlinformation, data, or control information and data within a TTI lessthan or equal to 1 ms, and the second type UE may refer to a UE that cantransmit control information, data, or control information and datawithin a TTI of 1 ms. The shortened-TTI UE may be used interchangeablywith the first type UE, and the normal-TTI UE may be usedinterchangeably with the second type UE. Additionally, in the presentinvention, the terms “shortened-TTI”, “shorter-TTI”, “shortened TTI”,“shorter TTI”, “short TTI” and “sTTI” have the same meaning and may beused interchangeably. The terms “normal-TTI”, “normal TTI”, “subframeTTI” and “legacy TTI” have the same meaning and may be usedinterchangeably.

In the present invention, the first type UE may receive conventional SIBtransmission or paging information with an existing TTI of 1 ms.

In the present invention, for the first type UE, the TTI length fordownlink transmission may be different from that for uplinktransmission. For example, two OFDM symbols may become a TTI for thedownlink, and a slot of 0.5 ms may become a TTI for the uplink.

In the present invention, the short TTI is set so as not to cross theboundary of the existing subframe. However, in a different embodiment,the subframe may specify an additional OFDM symbol as a short TTI.

In the following description, shortened-TTI transmission may be referredto as first type transmission, and normal-TTI transmission may bereferred to as second type transmission. In the first type transmission,a control signal, a data signal, or control and data signals may betransmitted within a TTI less than 1 ms. In the second typetransmission, a control signal, a data signal, or control and datasignals may be transmitted within a TTI of 1 ms. In the description, theterms “shortened-TTI transmission” and “first type transmission” may beused interchangeably, and the terms “normal-TTI transmission” and“second type transmission” may be used interchangeably. The first typeUE may support both the first type transmission and the second typetransmission or may support the first type transmission only. The secondtype UE may support the second type transmission only and cannot supportthe first type transmission. In the present invention, for ease ofdescription, the phrase “for the first type UE” may be understood as“for the first type transmission”.

In the present invention, the TTI in the downlink may refer to a unitfor transmitting a control signal and data signal or for transmitting adata signal. For example, in the downlink of the existing LTE system,the TTI is a subframe of 1 ms. The TTI in the uplink may refer to a unitfor transmitting a control signal or a data signal. For example, in theuplink of the existing LTE system, the TTI is a subframe of 1 ms(identical to the downlink).

In the present invention, the term “shortened-TTI mode” indicates asituation where the UE or BS sends or receives a control or data signalaccording to a shortened-TTI unit, and the term “normal-TTI mode”indicates a situation where the UE or BS sends or receives a control ordata signal according to a subframe unit.

In the present invention, the term “shortened-TTI data” refers to datasent on the PDSCH or PUSCH sent or received according to a shortened-TTIunit, and the term “normal-TTI data” refers to data sent on the PDSCH orPUSCH sent or received according to a subframe unit. In the presentinvention, a downlink control signal for the shortened TTI indicates acontrol signal for shortened-TTI mode operations and may be referred toas sPDCCH or sEPDCCH; an uplink control signal for the shortened TTI maybe referred to as sPUCCH; and a control signal for the normal TTIindicates a control signal for normal-TTI mode operations. For example,in the existing LTE system, downlink and uplink control signals for thenormal TTI may include the PCFICH, PHICH, PDCCH, EPDCCH, and PUCCH.

In the present invention, the terms “physical channel” and “signal” inthe existing LTE or LTE-A system may be used interchangeably with theterm “data” or “control signal”. For example, the PDSCH being a physicalchannel to send normal-TTI data may be referred to as normal-TTI data;and the sPDSCH being a physical channel to send shortened-TTI data maybe referred to as shortened-TTI data. Similarly, in the presentinvention, shortened-TTI data sent in the downlink and the uplink may bereferred to as sPDSCH and sPUSCH, respectively.

As described above, the present invention defines transmission andreception operations for the shortened-TTI UE and the BS, and presents adetailed scheme that enables the existing UE and the shortened-TTI UE tocoexist in the same system. In the present invention, a normal-TTI UErefers to a UE that sends and receives control information and datainformation according to a subframe unit of 1 ms. The controlinformation for the normal-TTI UE may be carried by the PDCCH mapped tomaximum three OFDM symbols in one subframe or carried by the EPDCCHmapped to a specific RB in one entire subframe. A shortened-TTI UEindicates a UE that can not only send and receive according to asubframe unit as in the case of a normal-TTI UE but also send andreceive according to a time unit less than a subframe. A shortened-TTIUE may also indicate a UE that can support transmission and receptionaccording to a time unit less than a subframe only.

One of the features of the present invention is to provide a method thatdelivers uplink and downlink control information to a shortened-TTI UEusing a TTI less than 1 ms and enables the shortened-TTI UE to performdata transmission and reception. More specifically, the presentinvention is to provide a method that can allocate and determine PDCCH,EPDCCH, PUCCH, PDSCH and PUSCH resources for shortened-TTI transmission.A description is given of the time-frequency domain structure in the LTEsystem with reference to FIGS. 1, 2 and 3 .

FIG. 1 and FIG. 2 show the downlink frame structure and the uplink framestructure in the LTE or LTE-A system, respectively. The uplink and thedownlink are commonly composed of subframes of 1 ms or slots of 0.5 msin the time domain, and are respectively composed of N_(RB) ^(DL) RBsand N_(RB) ^(UL) RBs in the frequency domain.

FIG. 3A illustrates one PRB 301 of the time-frequency domain structureserving as a radio resource region for data or control channeltransmission in the downlink of the LTE system.

In FIG. 3A, the horizontal axis denotes the time domain and the verticalaxis denotes the frequency domain. In the LTE system, the TTI is onesubframe 300 corresponding to 1 ms. One subframe is composed of twoslots 305 and 307, and each slot includes 7 OFDM symbols. In thefrequency domain, one PRB 301 is composed of 12 consecutive subcarriers.A resource element (RE) 313 is defined by one OFDM symbol and onesubcarrier. One PRB is the basic unit for resource allocation in the LTEsystem. In one PRB with one subframe, 24 REs are used for CRS. Onesubframe includes total 14 OFDM symbols, and 1, 2 or 3 OFDM symbols maybe used for PDCCH transmission. In FIG. 3A, one OFDM symbol is used forPDCCH transmission. Namely, in the existing LTE system, up to 3 OFDMsymbols in the fore part of a subframe may be used for downlink controlchannels.

FIG. 3B depicts a base station procedure carried out when the BSreceives UE capability information on capabilities supported by the UEfrom the UE.

Upon reception of UE capability information from a UE, if support ofshortened-TTI transmission is indicated by the received UE capabilityinformation (362), the BS provides the UE with both normal-TTIinformation and shortened-TTI information through higher layer signaling(364). If support of shortened-TTI transmission is not indicated by thereceived UE capability information (362), the BS determines that the UEdoes not support the shortened-TTI transmission and provides the UE withonly normal-TTI information through higher layer signaling (366).

FIG. 3C depicts a procedure used by the UE to send UE capabilityinformation to the BS.

If the UE is capable of supporting the shortened-TTI transmission (381),it sends the BS UE capability information containing an indication tothe capability of shortened-TTI transmission (383). If the UE does notsupport the shortened-TTI transmission (381), it sends the BS UEcapability information without an indication to the capability ofshortened-TTI transmission (385).

In the above description, the UE is depicted as sending UE capabilityinformation containing information related to the shortened-TTItransmission, and the BS is depicted as receiving information related tothe shortened-TTI transmission via UE capability information. However,the BS may receive information indicating supportability of theshortened-TTI transmission from the UE by use of various other schemes.

First, in the present invention, to support transmission and receptionbased on a slot unit, transmission and reception operations of theshortened-TTI UE and the BS are defined and a scheme is proposed thatenables the normal-TTI UE and the shortened-TTI UE to operate togetherin the same system. That is, in FIG. 3A, the first slot 305 of asubframe is a transmission interval, and the second slot 307 thereof isthe next transmission interval. Although only one PRB is shown in FIG.3A for brief description, this may be repeated for N_(RB) RBs.

To achieve transmission and reception according to a slot unit, controland data signals for the uplink and the downlink should be included ineach slot. A scheme for including control and data signals for theuplink and the downlink in the first slot and second slot of a subframeis described later as a specific embodiment. In the present invention,the number of RBs used for transmission and reception may be greaterthan or equal to 6 and less than 110 without any limitation.

Meanwhile, in one embodiment, a UE having received scheduling accordingto a 1 ms TTI in the first slot of a subframe may not decode controlinformation in the second slot. In another embodiment, a UE havingreceived scheduling according to a 0.5 ms TTI in the first slot of asubframe can try to decode control information in the second slot.However, this is an illustrative example and the present invention isnot limited to or by the above operations.

First Embodiment

The first embodiment relates to a shortened-TTI transmission schemewhere the BS sends downlink control information for shortened-TTI UEs inthe first slot of each subframe by use of a specific DCI format. Forexample, the DCI format serving as scheduling information (DL grant) forshortened-TTI downlink data may be configured to fully or partiallyinclude the following control information.

-   -   Resource allocation type 0/1 flag: this indicates whether the        resource allocation scheme is of type 0 or type 1. Type 0        indicates resource allocation in the unit of Resource Block        Group (RBG) by use of a bitmap. In the LTE system, the basic        scheduling unit is a RB represented as a time-frequency domain        resource. An RBG including multiple RBs is the basic scheduling        unit for type 0. Type 1 indicates allocation of a specific RB in        one RBG.    -   Resource block assignment: this indicates an RB allocated for        data transmission. The resource represented by resource block        assignment is determined according to the system bandwidth and        resource allocation scheme. Here, the resource is an RB        corresponding only to the first slot.    -   Modulation and coding scheme (MCS): this indicates the        modulation scheme applied for data transmission and the        transport block size for data to be sent.    -   HARQ process number, this indicates the process number of the        corresponding HARQ process.    -   New data indicator: this indicates either initial transmission        for HARQ or retransmission.    -   Redundancy version: this indicates the redundancy version for        HARQ.    -   TPC command for PUCCH: this indicates a TPC command for Physical        Uplink Control Channel (PUCCH) being an uplink control channel.    -   Shortened-TTI indicator: this indicates whether shortened-TTI        transmission or existing transmission applies. That is, this        indicates whether the allocated resource is associated with        either one subframe or the first slot. If shortened-TTI        transmission does not apply, the shortened-TTI indicator may be        absent or set to a specific value. The shortened-TTI indicator        may be a 1-bit value indicating whether shortened-TTI        transmission applies, or may be a 2 or 3-bit value indicating        the TTI length. For example, when TTI lengths available to first        type UEs include subframe, slot, 2 symbols and 1 symbol, the        shortened-TTI indicator may be 2 bits wide. The shortened-TTI        indicator may be referred to as a TTI length indicator.

The DCI format described above explicitly includes the shortened-TTIindicator for shortened-TTI control information. Hence, the DCI formatcontaining normal-TTI control information is different from thatcontaining shortened-TTI control information, which enables a UE todistinguish between normal-TTI control information and shortened-TTIcontrol information by checking the DCI format.

As described above, the shortened-TTI indicator is separately definedfor the DCI format. However, the present invention is not necessarilylimited thereto. For example, reuse of an existing field can beconsidered for notifying shortened-TTI transmission.

The DCI is appended by a CRC value using a specific RNTI, channel coded,rate matched, modulated, and transmitted via the PDCCH. The PDCCH ismapped to up to the first three OFDM symbols in the first slot fortransmission.

FIG. 4 depicts a procedure for the BS to transmit shortened-TTI downlinkcontrol information to the UE according to the first embodiment of thepresent invention.

Referring to FIG. 4 , the BS notifies the UE of the search spaceindicating the resource that can carry downlink control informationthrough higher layer signaling (400). The BS may determine the number ofOFDM symbols to be used for PDCCH transmission (1, 2, or 3) inconsideration of the amount of control information to be sent in thecurrent subframe. Control information for a shortened-TTI UE is encodedin a shortened-TTI DCI format (404), appended by a CRC value using aC-RNTI, channel encoded, mapped to PDCCH resources (406) together withcontrol information for other UEs, and transmitted. Control informationfor a normal-TTI UE is encoded in a normal-TTI DCI format (408),appended by a CRC value using a C-RNTI, channel encoded, mapped to PDCCHresources (406) together with control information for other UEs, andtransmitted. Here, the above C-RNTIs may have different type values.

FIG. 5 depicts a procedure for the UE to distinguish betweenshortened-TTI control information and normal-TTI control informationafter PDCCH reception according to the first embodiment of the presentinvention.

Referring to FIG. 5 , the shortened-TTI UE performs PDCCH reception inthe PDCCH resource region (500) and performs channel decoding byassuming that a PDCCH carrying a shortened-TTI DCI format is present.The UE performs blind decoding to identify the DCI through CRC checkingusing a specific C-RNTI (502). The UE determines whether a shortened-TTIindicator is present in the DCI information (504) to identify ashortened-TTI transmission.

If a shortened-TTI indicator is present, the UE determines that the DCIis control information for shortened-TTI transmission and reception(506). Thereafter, the UE performs PDSCH data decoding in thecorresponding slot according to the control information or performs anuplink operation for shortened-TTI transmission and reception in thecorresponding slot (508).

Here, performing an uplink operation in the corresponding slot mayindicate performing a HARQ feedback operation for a shortened-TTItransmission. For example, in the case of FDD mode, a UE performing anuplink operation for shortened-TTI transmission and reception may sendHARQ feedback information to the BS in a slot that is four slots afterthe slot where the PDSCH is received. In another embodiment, a UEperforming shortened-TTI transmission and reception may perform arelated art HARQ feedback operation by sending HARQ feedback informationto the BS at a subframe that is four subframes after the subframeincluding the corresponding slot.

If a shortened-TTI indicator is not present (existing subframe-unit TTItransmission), the UE determines that the DCI is control information fornormal-TTI transmission (510). Thereafter, the UE performs PDSCH datadecoding in the corresponding subframe or performs an uplink operationfor normal-TTI transmission and reception in the corresponding subframe(512).

The first embodiment may have several variations. For example, toindicate shortened-TTI control information, the shortened-TTI DCI formatmay be designed to include a shortened-TTI indicator whose length inbits may be set to one of 1, 2 and 3. As another example, theshortened-TTI DCI format may be designed so that the shortened-TTIindicator occupies a specified position in the DCI. For instance, whenthe corresponding DCI is shortened-TTI control information, the bit atthe position designated for the shortened-TTI indicator in theshortened-TTI DCI format may be set to 1.

Second Embodiment

The second embodiment relates to a shortened-TTI transmission schemewhere the DCI having shortened-TTI control information is implicitlyencoded without use of separate bits indicating shortened-TTItransmission. The second embodiment is described with reference to FIG.6 .

FIG. 6 depicts a procedure for the BS to allocate downlink controlresources for shortened-TTI transmission to the UE according to thesecond embodiment of the present invention.

In the second embodiment, the BS notifies the UE or a UE group of ashortened-TTI RNTI value or a range of shortened-TTI RNTI values throughhigher layer signaling (600). Thereafter, to configure shortened-TTIdownlink control information in a DCI format, the BS may generate theDCI so that a shortened-TTI indicator is not included or generate theDCI using an existing DCI format of the LTE system.

For shortened-TTI transmission, the BS appends a CRC value using ashortened-TTI RNTI different from a normal-TTI C-RNTI to the DCI, andapplies channel encoding to the DCI (604). For normal-TTI transmission,the BS appends a CRC value using a C-RNTI to the DCI, and applieschannel encoding to the DCI (608).

Thereafter, the resulting control information is mapped to PDCCHresources (606) for transmission.

The shortened-TTI RNTI may be different from the normal-TTI RNTI such asC-RNTI. For example, for shortened-TTI transmission, RNTI values between003D and FFF3 (in hexadecimal notation) may be assigned to UEs. Thechannel-encoded DCI is mapped to PDCCH resources together with controlinformation for other UEs. Different shortened-TTI RNTI values may beassigned to different first-type UEs, or the same shortened-TTI RNTIvalue may be assigned to a group of first-type UEs.

Then, the UE decodes the PDCCH region in the search space by use of ashortened-TTI RNTI. For example, A-bit control information, 16 paritybits for CRC appending, and a 16-bit RNTI value can be represented belowin Equation 1, Equation 2, and Equation 3.b ₀ ,b ₁ ,b ₂ ,b ₃ , . . . ,b _(A−1)  [Equation 1]p ₀ ,p ₁ ,p ₂ ,p ₃ , . . . ,p ₁₅  [Equation 2]x _(mti,0) ,x _(mti,1) , . . . ,x _(mti,15)  [Equation 3]

When control information B (in bits), 16 parity bits for CRC appending,and a 16-bit RNTI value are given by Equations 1 to 3, (A+16)-bit c₀,c₁, c₂, c₃, . . . , c_(A+15) after CRC appending using the RNTI valueare given below by Equation 4.c _(k) =b _(k) for k=0, 1, 2, . . . , A−1c _(k)=(b _(k) +x _(mti,k−A))mod 2 for k=A,A+1,A+2, . . .,A+15  [Equation 4]

In the above example, the BS may set a shortened-TTI RNTI value tox_(mti,0), x_(mti,1), . . . , x_(mti,15) for shortened-TTI transmission,and set a normal-TTI RNTI value to x_(mti,0), x_(mti,1), . . . ,x_(mti,15) for normal-TTI transmission.

FIG. 7 depicts a procedure for the UE to receive shortened-TTI controlinformation and data according to the second embodiment of the presentinvention.

Referring to FIG. 7 , the shortened-TTI UE performs PDCCH reception inthe PDCCH resource region (700) and performs channel decoding. The UEattempts to perform CRC decoding by use of a shortened-TTI RNTI notifiedin advance through higher layer signaling (702).

If CRC decoding is successful, the UE determines that the DCI is controlinformation for shortened-TTI transmission (704). Thereafter, the UEperforms PDSCH data decoding in the corresponding slot according to theDCI format and information or performs an uplink operation forshortened-TTI transmission and reception in the corresponding slot(706).

If CRC decoding using the shortened-TTI RNTI is unsuccessful, the UEattempts to perform CRC decoding by use of a normal-TTI RNTI (708). IfCRC decoding using the normal-TTI RNTI is successful, the UE determinesthat the DCI is a control signal for normal-TTI transmission (710).Thereafter, the UE performs PDSCH data decoding in the correspondingsubframe according to the DCI format and information or performs anuplink operation for normal-TTI transmission and reception in thecorresponding subframe (712).

The second embodiment may have several variations. For example, the BSmay notify a shortened-TTI UE of a specific shortened-TTI RNTI value ora range of shortened-TTI RNTI values through higher layer signaling. Asanother example, the UE is depicted in FIG. 7 as attempting CRC decodingusing a higher-layer-signaled shortened-TTI RNTI first. However, the UEmay perform blind decoding using a normal-TTI RNTI first, and, ifunsuccessful, then may perform blind decoding using a shortened-TTIRNTI. Alternatively, the UE may perform blind decoding using anormal-TTI RNTI and blind decoding using a shortened-TTI RNTI at thesame time.

Third Embodiment

The third embodiment relates to a method where the BS configures asearch space through which a shortened-TTI PDCCH can be transmitted andnotifies one UE or all UEs of the search space through higher layersignaling. The third embodiment is described with reference to FIG. 8 .

FIG. 8 depicts a procedure for the BS to transmit control informationfor shortened-TTI transmission and reception according to the thirdembodiment of the present invention.

In the third embodiment, the BS configures a search space through whicha shortened-TTI PDCCH can be transmitted and notifies the search spaceto a shortened-TTI UE through higher layer signaling (800). The BSappends a CRC value to the DCI including a control resource indicatingshortened-TTI transmission and applies channel encoding to the DCI(802). The BS maps the PDCCH to the search space (806), and does not mapnormal-TTI control resources to the search space (808).

Downlink control information is sent in a unit of Control ChannelElement (CCE). One PDCCH may be carried by 1, 2, 4, or 8 CCEs, and thenumber of CCEs used to carry the PDCCH is referred to as the aggregationlevel. The search space indicates a set of CCEs that can be monitored bya UE attempting blind decoding for downlink control information. In thefollowing description, the search space with aggregation level L∈{1, 2,4, 8} is denoted by S_(k) ^((L)). For normal-TTI transmission to anormal-TTI UE or shortened-TTI UE, the CCE number indicating the searchspace with aggregation level L is given by Equation 5.L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i, i=, . . . , L−1  [Equation 5]

In the above equation, N_(CCE,k) indicates the total number of CCEs inthe control region of k^(th) subframe. In the case of m′, for the commonsearch space used by all UEs in the cell, m′=m; and, for the UE-specificsearch space given to a particular UE, if the carrier indicator field(CIF) n_(CI) is set, m′=m+M^((L))*n_(CI) and if CIF n_(CI) is not set,m′=m. Here, m=0, . . . , M^((L))−1 and M^((L)) is the number of PDCCHsto be monitored in the given search space. In the case of Y_(k), for thecommon search space, Y_(k)=0; and, for the UE-specific search space,Y_(k)=(A*Y_(k−1)) mod D, where Y⁻¹=n_(RNTI)≠0, A=39827, D=65537,k=└n_(s)/2┐. Here, n_(RNTI) indicates a RNTI value assigned to the UE.

For shortened-TTI transmission to a shortened-TTI UE, the CCE numberindicating the search space carrying downlink control information may beset differently from that for a normal-TTI UE, so that shortened-TTItransmission and normal-TTI transmission can be distinguished.

For example, the CCE number indicating the search space allocated totransmit downlink control information for shortened-TTI transmission canbe given by the following equation.L{(Y _(k) ^(shortened-TTI) +m′)mod └N _(CCE,k) /L}+i,i=0, . . .,L−1  [Equation 6]

In Equation 6, in the case of Y_(k) ^(shortened-TTI), for the commonsearch space, Y_(k)=c; and, for the UE-specific search space,Y_(k)=(A*Y_(k−1))mod D, where Y⁻¹=n_(RNTI)+c≠0, A=39827, D=65537, andk=└n_(s)/2┘. Here, n_(RNTI) indicates a RNTI value assigned to the UE,and c is a value selected from among nonzero integers. Use of constant cin the formation of the search space for shortened-TTI transmissionenables a differentiation between the search space for normal-TTItransmission and the search space for shortened-TTI transmission.

As another example, the CCE number indicating the search space allocatedto transmit downlink control information for shortened-TTI transmissioncan be given by the following equation.L{(Y _(k) +m ^(shortened-TTI))mod └N _(CCE,k) /L}+i,i=0, . . .,L−1  [Equation 7]

In the above equation, in the case of m′^(shortened-TTI), for the commonsearch space used by all UEs in the cell, m′^(shortened-TTI)=m+c; and,for the UE-specific search space given to a particular UE, if thecarrier indicator field (CIF) n_(CI) is set,m^(shortened-TTI)=m+M^((L))*n_(CI)+c and if CIF n_(CI) is not set,m′^(shortened-TTI)=m+c. Here, m=0, . . . , M^((L))−1; M^((L)) is thenumber of PDCCHs to be monitored in the given search space; and c is avalue selected from among nonzero integers.

Equation 6 and Equation 7 are illustrations for configuring differentsearch spaces for normal-TTI transmission and shortened-TTItransmission. The above equations can be modified in various ways toenable a differentiation between the search space for normal-TTItransmission and the search space for shortened-TTI transmission.Meanwhile, in the second embodiment, assigning a separate shortened-TTIRNTI may enable a differentiation between search spaces.

FIG. 9 depicts a procedure for the UE to receive a shortened-TTI controlsignal according to the third embodiment of the present invention.

Referring to FIG. 9 , a shortened-TTI UE receives information on asearch space through which a shortened-TTI PDCCH can be sent from the BSthrough higher layer signaling (900).

The UE receives the PDCCH (902) and performs blind decoding in aspecific search space.

If PDCCH decoding in the shortened-TTI search space (904) is successful(906), the UE determines that the control information carried by thecorresponding PDCCH is control information for shortened-TTItransmission (908), and performs PDSCH data decoding in thecorresponding slot according to the DCI format and information orperforms an uplink operation for shortened-TTI transmission andreception in the corresponding slot (910).

If PDCCH decoding in the normal-TTI search space is successful (912),the UE determines that the control information carried by thecorresponding PDCCH is control information for normal-TTI transmission(914), and performs PDSCH data decoding in the corresponding subframeaccording to the DCI format and information or performs an uplinkoperation for normal-TTI transmission and reception in the correspondingsubframe (916).

Fourth Embodiment

The fourth embodiment relates to a method where the BS configures aresource block to which a shortened-TTI PDSCH can be mapped and notifiesa UE or all UEs of the resource block through higher layer signaling,and a shortened-TTI UE recognizes PDSCH reception in the shortened-TTIresource block as shortened-TTI transmission. The fourth embodiment isdescribed with reference to FIG. 10 .

FIG. 10 depicts a procedure for the BS to transmit a shortened-TTI PDSCHaccording to the fourth embodiment of the present invention.

In the fourth embodiment, the BS configures a resource block in which ashortened-TTI PDSCH can be allocated and notifies a shortened-TTI UE ofthe resource block through higher layer signaling (1000). Theinformation on the resource block may be applied commonly to all UEsmanaged by the BS or be applied specifically (dedicatedly) to ashortened-TTI UE.

To transmit a shortened-TTI PDSCH (1002), the BS includes allocationinformation on the resource block configured for PDSCH transmission inthe DCI (1004) and maps the resulting DCI to PDCCH resources (1008) fortransmission. To transmit a normal-TTI PDSCH (1002), the BS includesallocation information on a resource block configured fornon-shortened-TTI PDSCH transmission in the DCI (1004) and maps theresulting DCI to PDCCH resources (1008) for transmission.

FIG. 11 depicts a procedure for the UE to receive a shortened-TTIcontrol signal according to the fourth embodiment of the presentinvention.

Referring to FIG. 11 , a shortened-TTI UE receives information on aresource block through which a shortened-TTI PDSCH can be sent from theBS through higher layer signaling (1100).

The UE performs PDCCH decoding in the corresponding slot (1104) andidentifies allocation information on a resource block used for PDSCHtransmission in the PDCCH (1106). If the resource block, used for PDSCHtransmission, indicated by the identified allocation information matchesthe resource block, through which a shortened-TTI PDSCH can be sent,notified by the BS through higher layer signaling, the UE determinesthat the control information carried by the corresponding PDCCH iscontrol information for shortened-TTI transmission (1108), and performsPDSCH data decoding in the corresponding slot according to the DCIformat and information or performs an uplink operation for shortened-TTItransmission and reception in the corresponding slot (1110).

If the resource block, used for PDSCH transmission, indicated by theidentified allocation information does not match the resource block,through which a shortened-TTI PDSCH can be sent, notified by the BSthrough higher layer signaling, the UE determines that the controlinformation carried by the corresponding PDCCH is control informationfor normal-TTI transmission (1112), and performs PDSCH data decoding inthe corresponding subframe according to the DCI format and informationor performs an uplink operation for normal-TTI transmission andreception in the corresponding subframe (1114).

Fifth Embodiment

The fifth embodiment relates to a method for downlink controlinformation transmission where the BS configures an RB range, includingup to the first three OFDM symbols of the second slot of a subframe, towhich shortened-TTI control information can be mapped or configures aset of such RB ranges and notifies a UE or all UEs of the RB range orthe RB range set through higher layer signaling, and a shortened-TTI UEperforms blind decoding within the RB range or sequentially performsblind decoding within each RB range belonging to the RB range set. Thefifth embodiment is described with reference to FIG. 12 . In thisembodiment, the RB refers to the PRB or VRB.

FIG. 12 depicts a procedure for the BS to transmit a shortened-TTIcontrol resource in the second slot of each subframe according to thefifth embodiment of the present invention.

In the fifth embodiment, the BS configures a resource block throughwhich a shortened-TTI control resource is to be transmitted in thesecond slot of each subframe and notifies the resource block to eachshortened-TTI UE through higher layer signaling (1200). A description isgiven of a scheme for configuring a resource block through which ashortened-TTI control resource is to be transmitted and signaling theresource block to the UE with reference to FIG. 13 , FIG. 14 , and FIG.15 .

FIG. 13 illustrates regions to which downlink control resources for theshortened-TTI UE can be mapped according to the fifth embodiment of thepresent invention. In FIG. 13 , up to the first three OFDM symbols ofthe second slot can be a region to which downlink control resources fora shortened-TTI UE can be mapped. First, among N_(RB) ^(DL) RBsconstituting the whole frequency domain, a first RB range to which thePDCCH for a shortened-TTI UE can be mapped is formed to include N_(RB)^(shortTTI,1) RBs. Next, a second RB range to which the PDCCH for ashortened-TTI UE can be mapped is formed to include N_(RB) ^(shortTTI,2)RBs among N_(RB) ^(DL) RBs constituting the whole frequency domain. Inthis way, for mapping the PDCCH for shortened-TTI UEs, it is possible toform L RB ranges respectively including N_(RB) ^(shortTTI,1) RBs, N_(RB)^(shortTTI,2) RBs, . . . , N_(RB) ^(shortTTI,L) RBs among N_(RB) ^(DL)RBs. Here, L is an integer greater than or equal to 1. When one of theRB ranges is higher-layer signaled by the BS to a shortened-TTI UE, theUE configures the higher-layer signaled value N_(RB) ^(shortTTI) as thenumber of RBs used to map control signals in the second slot. Instead ofsignaling one RB range, when L RB ranges (a set of RB ranges) arehigher-layer signaled by the BS to a shortened-TTI UE, the UE selectsone of the L RB ranges and configures the selected value N_(RB)^(shortTTI) as the number of RBs used to map control signals in thesecond slot. Thereafter, if blind decoding in the selected RB range isunsuccessful, the UE selects another one of the L RB ranges andconfigures the selected value N_(RB) ^(shortTTI) as the number of RBsused to map control signals in the second slot. The UE may repeat theabove process.

The above scheme for configuring RB ranges to which the PDCCH forshortened-TTI UEs can be mapped and higher-layer signaling the same canbe modified in various ways. For example, referring to FIG. 14 , the RBsto which the PDCCH for shortened-TTI UEs can be mapped may be allocatedas N_(RB) ^(shortTTI,i) RBs (1412) distributed in the overall downlinkfrequency domain. As another example, referring to FIG. 15 , theresource region 1512 containing up to the first three OFDM symbols inthe second slot of each subframe may be subdivided in the frequencydomain into L RB groups including N_(RB) ^(shortTTI,1) RBs, N_(RB)^(shortTTI,2) RBs, . . . , N_(RB) ^(shortTTI,L) RBs, respectively (1514,1516, 1518).

In addition to the schemes described above, the block of resourcescorresponding to up to the first three OFDM symbols in the second slotof each subframe can be divided in the frequency domain so as to mapcontrol signals for shortened-TTI UEs in a variety of other ways.

Accordingly, the BS determines whether to higher-layer signal one valueN_(RB) ^(shortTTI) being the number of RBs usable for mapping controlsignals for shortened-TTI UEs or a set of values N_(RB) ^(shortTTI) eachbeing the number of RBs usable for mapping control signals forshortened-TTI UEs (1200). When the BS supports only one of one-valuesignaling and multi-value signaling described above, it may use thesupported signaling scheme. According to the determination result, theBS notifies one value N_(RB) ^(shortTTI) (RB count) to the UE throughhigher layer signaling (1202) or notifies a set of values N_(RB)^(shortTTI) (RB counts) to the UE through higher layer signaling (1212).To higher-layer signal a set of values N_(RB) ^(shortTTI) (1212), the BSselects one from the set of values as N_(RB) ^(shortTTI) (1216). Toperform downlink control resource mapping for shortened-TTI UEs withrespect to the value of N_(RB) ^(shortTTI) (1204, 1214), the BS composesthe PDCCH carrying downlink control information, the PHICH carryingACK/NACK information for uplink HARQ, and the PCFICH carryinginformation on the number of OFDM symbols used for control informationmapping in the corresponding slot, and maps the PDCCH, PHICH and PCFICHto the allocated RBs. Here, the process for composing the PDCCH, PHICH,PCFICH for shortened-TTI UEs (1206, 1218) and mapping these channels toboth up to the first three OFDM symbols in the second slot of eachsubframe and the RBs allocated for shortened-TTI control signaltransmission (1208, 1220) follows the process used by the BS to composethe PDCCH, PHICH and PCFICH for normal-TTI UEs and map these channels toup to the first three OFDM symbols of each subframe with substitutingN_(RB) ^(shortTTI) for N_(RB) ^(DL) (total number of downlink RBs)(1208, 1220). Unlike normal-TTI transmission, the PHICH and PCFICH maybe omitted for shortened-TTI transmission. In this case, the regionassigned to the omitted PHICH and PCFICH may be used to transmit thePDCCH. Information on the omitted PHICH and PCFICH may be notified bythe BS to the UE through higher layer signaling or through a procedurepre-agreed between the BS and the UE.

When N_(RB) ^(shortTTI) RBs are used to transmit shortened-TTI controlinformation, the RB number for these RBs may be assigned in the rangefrom 0 to N_(RB) ^(shortTTI)−1 according to the existing PRB numbers inascending or descending order. For normal-TTI UE control information, nooperation is newly initiated in the second slot of each subframe (1210,1222).

In the above description, the RB range is depicted as being used forcontrol information transmission in the second slot of a subframe. Inthis case, the RB range used to transmit data scheduled by the controlinformation may also be a problem. In one embodiment, the data scheduledby specific control information can be sent through the same RB range asthat used to transmit the control information. In another embodiment,the data scheduled by specific control information can be sent throughany RB range regardless of or other than the RB range used to transmitthe control information.

FIG. 16 depicts a procedure for the UE to receive shortened-TTI controlsignals sent in the second slot of each subframe according to the fifthembodiment of the present invention.

Referring to FIG. 16 , a shortened-TTI UE receives information on an RBrange (through which control information is to be sent in the secondslot of each subframe) and the number of RBs or information on a set ofRB ranges and the number of RB ranges from the BS through higher layersignaling (1600).

Upon reception of information on an RB range (through which controlinformation is to be sent in the second slot of each subframe) and thenumber of RBs (N_(RB) ^(shortTTI)), the UE temporarily substitutesN_(RB) ^(shortTTI) for N_(RB) ^(DL) for decoding in the second slot ofthe corresponding subframe (1602). Using the above values, the UEperforms, at the first OFDM symbol of the second slot, decoding on thePHICH carrying ACK/NACK information for uplink HARQ and the PCFICHcarrying information on the number of OFDM symbols used to map controlinformation in the corresponding slot (1604).

On the basis of the decoded PCFICH information, the UE performs blinddecoding on up to the first three OFDM symbols for PDCCH decoding(1606). If control information is obtained through successful blinddecoding (1608), the UE determines that the obtained control informationis control information for shortened-TTI transmission, and performsPDSCH data decoding in the corresponding slot according to the DCIformat and information or performs an uplink operation for shortened-TTItransmission and reception in the corresponding slot (1610).

Upon reception of information on a set of RB ranges (through whichcontrol information is to be sent in the second slot of each subframe)and the number of RB ranges from the BS through higher layer signaling,the UE selects one RB range from the set of RB ranges and sets the valueof N_(RB) ^(shortTTI) to the number of RBs belonging to the selected RBrange (1612).

The UE temporarily substitutes N_(RB) ^(shortTTI) for N_(RB) ^(DL) fordecoding in the second slot of the corresponding subframe (1614). Usingthe above values, the UE performs, at the first OFDM symbol of thesecond slot, decoding on the PHICH carrying ACK/NACK information foruplink HARQ and the PCFICH carrying information on the number of OFDMsymbols used to map control information in the corresponding slot(1616).

On the basis of the decoded PCFICH information, the UE performs blinddecoding on up to the first three OFDM symbols for PDCCH decoding(1618). If control information is obtained through successful blinddecoding (1620), the UE determines that the obtained control informationis control information for shortened-TTI transmission, and performsPDSCH data decoding in the corresponding slot according to the DCIformat and information or performs an uplink operation for shortened-TTItransmission and reception in the corresponding slot (1622).

Upon unsuccessful blind decoding, if there remains an RB notblind-decoded yet in the RB range (1624), the UE performs blind decodingagain on the remaining RB. If blind decoding has been unsuccessful onall RBs belonging to the RB range (1624), the UE newly selects one RBrange from the higher-layer signaled set of RB ranges and newlydetermines the value of N_(RB) ^(shortTTI) (1626). Thereafter, the aboveprocess is repeated until the control information is successfullyobtained or blind decoding is performed for all RB ranges in thehigher-layer signaled set.

The fifth embodiment may be modified and applied in various ways. Forexample, to configure L RB ranges with N_(RB) ^(shortTTI,1), N_(RB)^(shortTTI,2), . . . , N_(RB) ^(shortTTI,L) for PDCCH mapping forshortened-TTI UEs, the value of L may be set to 1 (L=1). That is, forshortened-TTI UEs, the BS may configure only one RB range for PDCCHmapping.

Sixth Embodiment

The sixth embodiment relates to a method where the BS configures asearch space to which a shortened-TTI EPDCCH (or enhanced controlinformation) can be mapped and notifies one UE or all UEs of the searchspace through higher layer signaling. The sixth embodiment is describedwith reference to FIG. 17 .

FIG. 17 depicts a procedure for the BS to transmit control informationfor shortened-TTI transmission and reception by use of shortened-TTIEPDCCH transmitted within one slot according to the sixth embodiment ofthe present invention.

In the sixth embodiment, the BS configures a search space through whicha shortened-TTI EPDCCH can be transmitted and notifies informationrelated to the search space to a shortened-TTI UE through higher layersignaling (1700). This higher layer signaling may carry informationregarding a subframe at which the EPDCCH can be sent, the OFDM symbolnumber at which the EPDCCH can start, an RB at which the EPDCCH can besent, the resource element index for transmitting uplink controlinformation for EPDCCH transmission, and the sequence index number fortransmitting an EPDCCH reference signal. The BS appends a CRC value tothe DCI including a control resource indicating shortened-TTItransmission and applies channel encoding to the DCI (1702). The BS mapsthe EPDCCH to the search space (1706), and does not map normal-TTIcontrol resources to the search space (1708). The search space withaggregation level L through which a shortened-TTI EPDCCH can be sent maybe determined according to the following equation.

$\begin{matrix}{{{L\left\{ {\left( {Y_{p,k} + \left\lfloor \frac{m \cdot N_{{ECCE},p,k}}{L \cdot M_{p}^{(L)}} \right\rfloor + b + c} \right){mod}\left\lfloor {N_{{CCE},p,k}/L} \right\rfloor} \right\}} + i},{i = 0},\ldots,{L - 1}} & \left\lbrack {{Equation}8} \right\rbrack\end{matrix}$

In Equation 8, Y_(p,k)=(Ap·Y_(p,k−1))mod D where Y_(p,−1)=n_(RNTI)≠0,A₀=39827, A₁=39829, D=65537, and k=└n_(s)/2┘. Here, n_(s) is a slotnumber in a radio frame.

In the above equation, b is given by n_(CI) if the carrier indicatorfield (CIF) n_(CI) is set, and is given by 0 if CIF n_(CI) is not set.Here, m=0, . . . , M_(p) ^((L))−1 and M_(p) ^((L)) is the number ofPDCCHs to be monitored in each search space, and c is a value selectedfrom among nonzero integers.

Equation 8 is an illustration for configuring different EPDCCH searchspaces for normal-TTI transmission and shortened-TTI transmission. Theabove equation can be modified in various ways to enable adifferentiation between the EPDCCH search space for normal-TTItransmission and the EPDCCH search space for shortened-TTI transmission.Meanwhile, in the second embodiment, assigning a separate shortened-TTIRNTI may enable a differentiation between search spaces.

According to the sixth embodiment, in the first slot of a subframe,while control information for a normal-TTI UE is mapped to the firstthree OFDM symbols of the slot, the EPDCCH for a shortened-TTI UE ismapped to other OFDM symbols of the slot excluding the first three OFDMsymbols; and, in the second slot of the subframe, while controlinformation for a shortened-TTI is mapped to the first three OFDMsymbols of the slot and the EPDCCH for a shortened-TTI UE is mapped toother OFDM symbols of the slot excluding the first three OFDM symbols.

In the present invention, the shortened-TTI EPDCCH, like the existingnormal-TTI EPDCCH, is mapped in a unit of ECCE. However, while theexisting normal-TTI EPDCCH is mapped to ECCEs in the correspondingsubframe, the shortened-TTI EPDCCH is mapped to ECCEs in thecorresponding slot. The shortened-TTI ECCE is composed of resourceelements (REs) in the slot.

FIG. 18 depicts a procedure for the UE to receive a control signal sentfor shortened-TTI transmission according to the sixth embodiment of thepresent invention.

Referring to FIG. 18 , a shortened-TTI UE receives information on asearch space through which a shortened-TTI EPDCCH can be sent from theBS through higher layer signaling (1800).

The UE receives the EPDCCH (1802) and performs blind decoding in aspecific search space. If EPDCCH decoding in the shortened-TTI searchspace (1804) is successful (1806), the UE determines that the controlinformation carried by the corresponding EPDCCH is control informationfor shortened-TTI transmission (1808), and performs PDSCH data decodingin the corresponding slot according to the DCI format and information orperforms an uplink operation for shortened-TTI transmission andreception in the corresponding slot (1810).

If EPDCCH decoding in the normal-TTI search space is successful (1812),the UE determines that the control information carried by thecorresponding EPDCCH is control information for normal-TTI transmission(1814), and performs PDSCH data decoding in the corresponding subframeaccording to the DCI format and information or performs an uplinkoperation for normal-TTI transmission and reception in the correspondingsubframe (1816).

6.5^(th) Embodiment

The 6.5^(th) embodiment relates to a method for transmission where theBS maps the PDSCH for shortened-TTI UEs in a full subframe. The 6.5^(th)embodiment is described with reference to FIG. 20 . In this embodiment,the PDSCH for shortened-TTI UEs is mapped not only to a slot whereshortened-TTI control resources are transmitted but also to the nextslot after the slot where shortened-TTI control resources aretransmitted. In other words, the PDSCH for shortened-TTI UEs may bemapped for transmission to a resource block section occupying a fullsubframe where shortened-TTI control resources can be present.

FIG. 20 shows a downlink frame structure where one subframe is dividedfor RBs for shortened-TTI transmission and RBs for normal-TTItransmission. The region 2060 of up to the first three OFDM symbols inthe first slot is used to map control information for normal-TTI orshortened-TTI transmission. The region 2066 of up to the first threeOFDM symbols in the second slot is used to map control information forshortened-TTI transmission. Allocation of N_(RB) ^(shortTTL,i) RBsusable for mapping shortened-TTI control information may be performed ina manner similar to that of other embodiments described before.

Multiple RB sections to which shortened-TTI control information ismapped can be configured and allocated to UEs. The remaining downlinkinterval where shortened-TTI control information is not mapped may beused to map the PDSCH for normal-TTI transmission (2068).

The PDSCH indicated by shortened-TTI control information sent in thefirst slot may be mapped to a specific RB section of the correspondingslot for transmission; and the PDSCH indicated by shortened-TTI controlinformation sent in the second slot may be mapped to a specific RBsection of the corresponding slot for transmission.

As another example, at a resource block used to transmit shortened-TTIcontrol information to shortened-TTI UEs, the control information sentin the first slot (2060) may indicate resource blocks to transmit thePDSCH mapped in both the first slot and the second slot (2070).

How to map the PDSCH sent in both the first slot and the second slot maybe described in the following way.

To map the PDSCH with rate matching, it is possible to map the PDSCH tothe corresponding RB with rate matching by excluding the resource regionused to map second-slot shortened-TTI control information.

As another example, the PDSCH is rate-matched in a manner similar tothat for normal-TTI transmission, and mapped to the corresponding RB byexcluding the resource element used to transmit second-slotshortened-TTI control information through puncturing.

FIG. 21 depicts a procedure of the BS operating by use of the abovePDSCH mapping.

The BS allocates an RB to be used to send data to a shortened-TTI UE(2100). If the data is shortened-TTI data to be sent in one slot (2102),to allocate the PDSCH in the corresponding RB in the corresponding slot,the BS encodes the PDSCH with rate matching (2104) and maps the PDSCH toresource elements (2106). Thereafter, the BS maps shortened-TTI controlinformation to the (E)PDCCH (2108).

The BS sends the control signal and PDSCH data as determined above tothe UE (2110). If the data is shortened-TTI data to be sent in onesubframe (2102), the BS checks whether shortened-TTI control informationis present in the second slot of the corresponding RB used to send thedata (2112). If shortened-TTI control information is present in thesecond slot of the corresponding RB, the BS does not map the PDSCH tothe resource element used to map the shortened-TTI control information.

Not to map the PDSCH to the resource element to which the shortened-TTIcontrol information is mapped, the PDSCH may be rate-matched so that theresource element used to carry the shortened-TTI control information isexcluded (2114), or the PDSCH may be rate-matched in a regular way andthen the resource element used to carry the shortened-TTI controlinformation may be punctured (2116).

Upon mapping the PDSCH, the BS may send the corresponding resourceallocation information through a normal-TTI (E)PDCCH or a modifiedshortened-TTI (E)PDCCH (2118). Here, the modified shortened-TTI (E)PDCCHcorresponds to adding an extra bit, which notifies a shortened-TTI UEthat the PDSCH is mapped to a specific resource region occupying a fullsubframe, to the scheme for shortened-TTI (E)PDCCH mapping proposed in adifferent embodiment described before. If the data is not shortened-TTIdata (2102) and shortened-TTI control information is not present in thesecond slot of the corresponding RB, the BS encodes and rate-matches thePDSCH in a manner similar to that for normal-TTI transmission (2122) andmaps the resulting PDSCH to the corresponding resource element (2124).The BS maps the PDSCH allocation information to the normal-TTI (E)PDCCHfor transmission (2126).

FIG. 22 depicts a procedure performed by a shortened-TTI UE to determinethe region for PDSCH decoding upon receiving control information through(E)PDCCH blind decoding (2200).

Referring to FIG. 22 , when a shortened-TTI UE succeeds in decodingreceived downlink control information (2200), and if the controlinformation is for shortened-TTI control information (2202), the UEperforms PDSCH decoding in the slot where the control information isreceived (2204). If the control information is not for shortened-TTIcontrol information and the RB carrying the PDSCH is an RB havingshortened-TTI control information in the second slot (2206), the UEperforms PDSCH decoding on the RB except for the resource element towhich the second-slot shortened-TTI control information is mapped(2208).

If the control information is not for shortened-TTI control informationand the RB carrying the PDSCH is not an RB having shortened-TTI controlinformation in the second slot (2206), the UE performs PDSCH decoding onthe RB at the corresponding subframe (2210).

Seventh Embodiment

The seventh embodiment relates to a method where the BS notifiesinformation on an RB to which shortened-TTI EPDCCH can be mapped in eachslot through higher layer signaling and the UE receives downlink controlinformation through blind decoding of the EPDCCH. The seventh embodimentis described with reference to FIG. 19 .

That is, when control information is obtained from a higher-layersignaled RB range, the UE may regard the obtained control information asshortened-TTI control information.

FIG. 19 depicts a procedure for the BS to transmit shortened-TTI EPDCCHin each second slot according to the seventh embodiment of the presentinvention.

In the seventh embodiment, the BS configures an RB used to transmit ashortened-TTI control resource in each slot and notifies information onthe RB to shortened-TTI UEs through higher layer signaling (1900).

After configuring an RB to which a shortened-TTI control signal can bemapped, the BS maps the EPDCCH for shortened-TTI UEs to ECCEs (EnhancedControl Channel Element) of the configured RB for transmission in eachslot (1904). If shortened-TTI scheduling is not applied, the BS maps theEPDCCH for normal-TTI UEs to an RB configured to transmit a normal-TTIEPDCCH for transmission at each subframe (1906).

FIG. 23 depicts a procedure for the UE to receive a shortened-TTIcontrol signal sent at each slot according to the seventh embodiment ofthe present invention.

Referring to FIG. 23 , a shortened-TTI UE receives location informationof an RB through which control information is to be sent from the BS ineach slot through higher layer signaling (2300).

The UE performs blind decoding on the corresponding RB to decode theEPDCCH (2302). If control information is obtained through successfulblind decoding (2304), the UE determines that the obtained controlinformation is shortened-TTI control information, and performs PDSCHdata decoding in the corresponding slot according to the DCI format andinformation or performs an uplink operation for shortened-TTItransmission and reception in the corresponding slot (2306).

Next, a description is given of schemes for sending and receivingshortened-TTI uplink control resources through the PUCCH.

Meanwhile, according to one embodiment of the present invention, a UEperforming downlink reception based on shortened-TTI mode may performuplink transmission based on either shortened-TTI mode or normal-TTImode.

Eighth Embodiment

The eighth embodiment relates to a method for uplink control resourcetransmission and reception where, to send a shortened-TTI uplink controlresource through the PUCCH, a shortened-TTI UE may send the uplinkcontrol resource using one PRB during one slot, or the UE may send aportion of the uplink control resource using one PRB during up to thefirst six OFDM symbols of one slot, performs frequency hopping, and sendthe remaining portion of the uplink control resource using another PRBduring the remaining OFDM symbols of the slot. The eighth embodiment isdescribed with reference to FIGS. 24 and 25 .

FIG. 24 depicts a procedure for the BS to allocate resources to ashortened-TTI UE for shortened-TTI PUCCH transmission according to theeighth embodiment of the present invention.

Before describing the procedure in FIG. 24 , an example of a PUCCHtransmission structure for a shortened-TTI is described with referenceto FIG. 25 .

Referring to FIG. 25 , downlink HARQ ACK/NACK bits and/or CSIinformation bits 2502 are channel coded (2504). Here, channel coding mayinclude rate matching or interleaving.

The UE applies scrambling (2506). The UE modulates the scrambled signal(2508) to generate M_(symb) modulation symbols d(0), d(1), . . . ,d(M_(symb)−1). In FIG. 25 , M_(symb)=12. The modulation symbols aremapped to the slot 2524 used to transmit a shortened-TTI PUCCH through asignal processor 2512. Here, the signal processor 2512 for ashortened-TTI PUCCH may include a block-wise multiplier 2514, a DFT(Discrete Fourier Transform) block 2516, and an IFFT (Inverse FastFourier Transform) block 2518. In the block-wise multiplier 2514,length-5 orthogonal sequences (or orthogonal cover (OC)) [w(0), w(1),w(2), w(3), w(4)] are block-wise multiplied. When the last OFDM symbolis used for SRS transmission or is emptied to protect another UEperforming SRS transmission, the last OFDM symbol is not sent. In thiscase, length-4 orthogonal sequences are used. After processing of DFT(2516) and IFFT (2518), the resulting values are mapped respectively toSC-FDMA symbols for UCI transmission in the slot. Specifically, themodulation symbols d(0) to d(11) are block-wise multiplied by OCsequences to produce the following five symbol sequences.

[d(0)w(0), d(1)w(0), d(2)w(0), d(3)w(0), d(4)w(0), d(5)w(0), d(6)w(0),d(7)w(0), d(8)w(0), d(9)w(0), d(10)w(0), d(11)w(0)],

[d(0)w(1), d(1)w(1), d(2)w(1), d(3)w(1), d(4)w(1), d(5)w(1), d(6)w(1),d(7)w(1), d(8)w(1), d(9)w(1), d(10)w(1), d(11)w(1)],

[d(0)w(2), d(1)w(2), d(2)w(2), d(3)w(2), d(4)w(2), d(5)w(2), d(6)w(2),d(7)w(2), d(8)w(2), d(9)w(2), d(10)w(2), d(11)w(2)],

[d(0)w(3), d(l)w(3), d(2)w(3), d(3)w(3), d(4)w(3), d(5)w(3), d(6)w(3),d(7)w(3), d(8)w(3), d(9)w(3), d(10)w(3), d(11)w(3)],

[d(0)w(0), d(1)w(4), d(2)w(4), d(3)w(4), d(4)w(4), d(5)w(4), d(6)w(4),d(7)w(4), d(8)w(4), d(9)w(4), d(10)w(4), d(11)w(4)]

Thereafter, the individual symbol sequences are DFT and IFFT processedand mapped respectively to SC-FDMA symbols 2526, 2530, 2532, 2534 and2538 in the slot for UCI transmission. In the above process, DFT andIFFT processing may be omitted.

The RS signals used by the BS for channel estimation for UCI receptionare mapped respectively to SC-FDMA symbols 2528 and 2536 designated forRS signal transmission through an RS signal processor 2522. Here, the RSsignal processor 2522 includes an IFFT block 2520 and RS signalgenerators 2540 and 2542. Hence, the UE generates RS signals through theRS signal generators 2540 and 2542 using CAZAC sequences. The generatedRS signals are IFFT processed (2520) and mapped respectively to SC-FDMAsymbols 2528 and 2536 designated for RS signal transmission.

FIG. 26 is an example of a PUCCH transmission structure for ashortened-TTI according to the present invention.

Referring to FIG. 26 , downlink HARQ ACK/NACK bits and/or CSIinformation bits 2602 are channel coded (2604), scrambled (2606), andmodulated (2608) in the same way as that of FIG. 25 . In FIG. 26 , thenumber of modulation symbols M_(symb) is 5. The modulation symbols aremultiplied by length-12 CAZAC sequences (2614) and mapped respectivelyto SC-FDMA symbols 2626, 2630, 2632, 2634 and 2638 designated for UCItransmission in the slot.

The RS signals used by the BS for channel estimation for UCI receptionare mapped respectively to SC-FDMA symbols 2628 and 2636 designated forRS signal transmission through an RS signal processor 2622. Here, the RSsignal processor 2622 includes an IFFT block 2620 and RS signalgenerators 2640 and 2642. Hence, the UE generates RS signals through theRS signal generators 2640 and 2642 using CAZAC sequences. The generatedRS signals are IFFT processed (2620) and mapped respectively to SC-FDMAsymbols 2628 and 2636 designated for RS signal transmission.

FIG. 27 is another example of a PUCCH transmission structure for ashortened-TTI according to the present invention.

Referring to FIG. 27 , downlink HARQ ACK/NACK information of 1 or 2 bitsis modulated into one symbol. This symbol is multiplied by length-12CAZAC sequences (2714), and block-wise multiplied by length-5 orthogonalsequences (or orthogonal cover (OC)) [w(0), w(1), w(2), w(3), w(4)]through a block-wise multiplier (2716). The resulting values are mappedrespectively to SC-FDMA symbols 2726, 2730, 2732, 2734 and 2738designated for UCI transmission in the slot.

The RS signals used by the BS for channel estimation for UCI receptionare mapped respectively to SC-FDMA symbols 2728 and 2736 designated forRS signal transmission in the same manner as in FIG. 25 or 26 .

In the above examples of FIGS. 25, 26 and 27 , two OFDM symbols are usedfor RS signal transmission in one slot. However, the number or positionof OFDM symbols used for RS signal transmission in one slot may bevaried. For example, in FIGS. 25, 26 and 27 , among 7 OFDM symbols, thesecond and sixth OFDM symbols are used for RS signal transmission.However, this can be readily modified so that the third, fourth andfifth OFDM symbols are used for RS signal transmission. In this case, asfour OFDM symbols in the slot are not used for RS signal transmission,the length of orthogonal sequences used in the above examples is to be4. As another example, only the fourth OFDM symbol may be used for RSsignal transmission and the remaining 6 OFDM symbols may be used for UCItransmission.

When a shortened-TTI PUCCH format depicted in FIG. 25, 26 or 27 is used,the RB used in one slot may be selected in various ways. For example,referring to FIG. 28 , the UE may map the shortened-TTI PUCCH to, amongtotal N_(RB) ^(UL) uplink RBs 2800, the n^(th) PRB 2806 in a full slot2802 for uplink transmission.

As another example, when a shortened-TTI PUCCH format depicted in FIG.25, 26 or 27 is used, it is possible to map the shortened-TTI PUCCH totwo different PRBs for transmission as shown in FIG. 29 . In this case,a frequency diversity gain can be obtained.

Here, two PRBs may be selected in various ways. As a representativeexample, the n^(th) PRB 2904 and the m^(th) PRB 2906 may be selected fortransmission so that m=N_(RB) ^(UL)−n−1. As another example, for ashortened-TTI UE trying to select two PRBs for uplink control signaltransmission as shown in FIG. 29 , the shortened-TTI UE may map aportion of a normal-TTI PUCCH format, being sent through one PRB duringtwo slots, to be sent in the first slot to the n^(th) PRB 2904 used foruplink control signal transmission, and map another portion of thenormal-TTI PUCCH format to be sent in the second slot to the m^(th) PRB2906 used for uplink control signal transmission.

As another example for resource mapping of a shortened-TTI PUCCH format,frequency hopping may be applied within one slot 3002 as shown in FIG.30 . In FIG. 30 , the portion of a shortened-TTI PUCCH formatcorresponding to the first L OFDM symbols 3008 is mapped to the n₁ ^(th)PRB 3004 and the portion of the shortened-TTI PUCCH format correspondingto the remaining 7-L OFDM symbols 3010 is mapped to the n₂ ^(th) PRB3006 within the same slot.

The PRB number used for mapping described in the above examples of FIGS.28, 29 and 30 may be higher-layer signaled by the BS or may beexplicitly or implicitly delivered from the BS through a shortened-TTI(E)PDCCH used to transmit shortened-TTI downlink control resources.

When the shortened-TTI UE transmits both a shortened-TTI PUCCH formatand a shortened-TTI PUCCH in the same slot, the BS may performtransmission and reception of uplink control resources in the followingway.

Referring to FIG. 24 , the BS determines the number of RBs available tothe shortened-TTI PUCCH format (N_(RB) ^((shortend-TTI))) inconsideration of the number of shortened-TTI UEs and the number ofshortened-TTI UEs supporting carrier aggregation in the current cell,and notifies all shortened-TTI UEs in the cell of information on thenumber of RBs available to the shortened-TTI PUCCH format (N_(RB)^((shortend-TTI))) through higher layer signaling (2402). The BSallocates n_(PUCCH) ^((shortend-TTI))RBs for the shortened-TTI PUCCHformat to each shortened-TTI UE without exceeding the N_(RB)^((shortend-TTI))RBs, and notifies individual shortened-TTI UEs ofinformation on the RBs allocated as a shortened-TTI PUCCH formatresource through higher layer signaling (2404). Alternatively, the BSmay perform (E)PDCCH mapping implicitly according to the shortened-TTIPUCCH format resource allocated to each UE, enabling the UE to identifythe shortened-TTI PUCCH format resource.

FIG. 31 depicts a procedure for the UE to receive a shortened-TTIcontrol signal sent in each slot according to the eighth embodiment ofthe present invention.

Referring to FIG. 31 , a shortened-TTI UE receives information on thenumber of RBs through which a shortened-TTI PUCCH format is to be sentfrom the BS in each slot through higher layer signaling (3100).Thereafter, the shortened-TTI UE receives a shortened-TTI resourcewithin the RB range from the BS through higher layer signaling (3102).In one embodiment of the present invention, the shortened-TTI resourcemay be identified by a sequence number or sequence type used in the RBrange.

Thereafter, the shortened-TTI UE receives the (E)PDCCH, and, if blinddecoding of the (E)PDCCH is successful, obtains a shortened-TTI PUCCHresource indicated by the DCI (3106). The UE composes an uplink controlsignal in a shortened-TTI PUCCH format and maps the uplink controlsignal to the shortened-TTI PUCCH resource for transmission to the BS(3108). One of step 3102 and step 3106 for obtaining the shortened-TTIPUCCH resource may be skipped.

Ninth Embodiment

The ninth embodiment relates to a method where bits indicatinginformation on a resource block to which a shortened-TTI PUCCH can bemapped are explicitly added to the downlink control resource of theshortened-TTI PDCCH or EPDCCH. The ninth embodiment is described withreference to FIG. 32 .

FIG. 32 depicts a procedure for the BS to allocate and send ashortened-TTI PUCCH resource to the UE according to the ninth embodimentof the present invention.

Referring to FIG. 32 , the BS determines the number of RBs (N_(RB)^((shortend-TTI))) available to the shortened-TTI PUCCH format inconsideration of the number of shortened-TTI UEs and the number ofshortened-TTI UEs supporting carrier aggregation in the current cell,and notifies all shortened-TTI UEs in the cell of information on thenumber of RBs (N_(RB) ^((shortend-TTI))) available to the shortened-TTIPUCCH format through higher layer signaling (3202). The BS allocatesn_(PUCCH) ^((shortend-TTI))RBs for the shortened-TTI PUCCH format toeach shortened-TTI UE without exceeding the N_(RB) ^((shortend-TTI))RBs(3204). To notify each shortened-TTI UE of the allocated shortened-TTIPUCCH format resource, the BS includes the shortened-TTI downlinkcontrol resource and a shortened-TTI PUCCH resource indicator in the DCIformat (3208). Here, the shortened-TTI PUCCH resource indicator may beincluded using the TPC field of the existing DCI format or using newlyadded bits. This indicator explicitly notifies the UE of theshortened-TTI PUCCH format resource.

FIG. 33 depicts a procedure for the UE to receive a shortened-TTIcontrol signal sent in each slot and obtain a shortened-TTI PUCCHresource according to the ninth embodiment of the present invention.

Referring to FIG. 33 , a shortened-TTI UE receives information on thenumber of RBs through which a shortened-TTI PUCCH format is to be sentfrom the BS in each slot through higher layer signaling (3300).Thereafter, the shortened-TTI UE receives the (E)PDCCH, and, if blinddecoding of the (E)PDCCH is successful (3302), obtains a shortened-TTIPUCCH resource indicated by the DCI (3304). The UE composes an uplinkcontrol signal in a shortened-TTI PUCCH format and maps the uplinkcontrol signal to the shortened-TTI PUCCH resource for transmission tothe BS (3306).

Tenth Embodiment

The tenth embodiment relates to a method where the BS allocates resourceelements to which a shortened-TTI PUCCH and a normal-TTI PUCCH aremapped and higher-layer signals the allocated resources to the UE, andthe UE performs PUCCH transmission by use of the resources allocated bythe BS. The tenth embodiment is described with reference to FIG. 34 .

Note that, in the tenth embodiment, the BS may not separately notify theUE of the number of RBs available to shortened-TTI PUCCH formattransmission.

FIG. 34 depicts a procedure for the BS to allocate a shortened-TTI PUCCHresource to the UE according to the tenth embodiment of the presentinvention.

Referring to FIG. 34 , the BS allocates resource elements to which ashortened-TTI PUCCH and a normal-TTI PUCCH are mapped (3400).Thereafter, for shortened-TTI transmission, the BS higher-layer signalsthe resource element to which a shortened-TTI PUCCH is to be mapped(3404). For normal-TTI transmission, the BS higher-layer signals theresource element to which a normal-TTI PUCCH is to be mapped (3406).

FIG. 35 depicts a procedure for the UE to receive a shortened-TTIcontrol signal sent in each slot and send an uplink control signal byuse of a shortened-TTI PUCCH resource higher-layer signaled in advanceaccording to the tenth embodiment of the present invention.

Referring to FIG. 35 , the UE obtains a shortened-TTI PUCCH resourcefrom the BS via higher layer signaling (3502). The shortened-TTI PUCCHresource may be identified by n_((PUCCH)) ^((1,{tilde over (p)})),n_((PUCCH)) ^((2,{tilde over (p)})), and n_((PUCCH))^((3,{tilde over (p)})) according to PUCCH format 1, 2 and 3, and isdetermined through higher layer signaling. The shortened-TTI PUCCH sentduring one slot may be identified by a resource index n_((PUCCH))^((shortened-TTI,{tilde over (p)})) and be higher-layer signaled. Afterbeing higher-layer signaled, the UE receives a shortened-TTI PDCCH,EPDCCH, or PDSCH (3504), and may receive information on theshortened-TTI PUCCH resource from the downlink control signal (3506).For example, the UE may utilize the CCE number used for PDCCHtransmission to determine the PUCCH resource index as a function of theCCE number. Thereafter, the UE performs PUCCH transmission using thePUCCH resource index (3508).

Eleventh Embodiment

The eleventh embodiment relates to a method where the BS processes datapackets from the higher layer separately for shortened-TTI transmissionand normal-TTI transmission according to QoS (Quality of Service) ClassIdentifier (QCI). The eleventh embodiment is described with reference toFIG. 36 .

Referring to FIG. 36 , the BS receives a data packet and associated QCIinformation from the higher layer (3602). If the packet delay budget ofthe QCI information is less than a preset threshold (3604) and the datapacket is for a shortened-TTI UE (3606), the BS transmits the datapacket through shortened-TTI scheduling (3608). If the packet delaybudget of the QCI information is greater than the preset threshold(3604), the BS transmits the data packet through normal-TTI scheduling(3610). Here, the sequence of decisions at steps 3604 and 3606 may bereversed.

The value of the threshold referenced at step 3604 may be set by the BSin advance.

FIG. 37 depicts a procedure of the BS to process data packets from thehigher layer separately for shortened-TTI transmission and normal-TTItransmission.

As steps of FIG. 37 are similar to those of FIG. 37 , a repeateddescription is omitted. However, the difference is that the criterionfor determining whether a data packet is for shortened-TTI transmissionor for normal-TTI transmission (3704) is distinct (i.e. differentattribute of the QCI).

The attribute of the QCI usable as a criterion may include resourcetype, priority level, packet error loss rate, or service type (agreed inadvance).

Twelfth Embodiment

The twelfth embodiment relates to a method where the BS notifies a UEwhether the UE should operate in shortened-TTI transmission mode (firsttype UE mode) or in normal-TTI transmission mode (second type UE mode)through higher layer signaling before actual data transmission. Thetwelfth embodiment is described with reference to FIGS. 40 and 41 .

FIG. 40 is a flowchart depicting a procedure for the BS to notify ashortened-TTI UE of transmission mode through higher layer signaling.

The BS determines the UE to be scheduled next for shortened-TTI data(4002). For shortened-TTI operation, the BS notifies the determined UEof shortened-TTI transmission through higher layer signaling (4004).This higher layer signaling may carry information on the location of RBsthat can be sent in shortened-TTI mode and information on the locationof RBs to which a control signal for shortened-TTI mode is to be mapped.

For normal-TTI operation, the BS notifies the determined UE ofnormal-TTI transmission through higher layer signaling (4006).

In this embodiment, when shortened-TTI mode is notified by the BS to aUE that is operating in normal-TTI mode to send and receive a datasignal, to allow the UE to operate again in normal-TTI mode, the BS mayhave to notify the UE of normal-TTI mode through higher layer signaling.

The transmission mode may be changed in various ways. For example, theBS and the UE can make an agreement in advance that when shortened-TTImode is higher-layer signaled at a first point in time, the transmissionmode returns to normal-TTI mode after a given time from the first pointin time. Here, higher layer signaling may carry information on theduration for shortened-TTI mode operation or information on the time forreturning to normal-TTI mode.

In the above case, the BS may operate in normal-TTI mode for the UEafter the agreed time without separate higher layer signaling.

FIG. 41 is a flowchart depicting a procedure for a shortened-TTI UE toreceive a notification of shortened-TTI mode or normal-TTI mode from theBS through higher layer signaling.

When transmission mode is higher-layer signaled by the BS, the UEdetermines whether shortened-TTI mode or normal-TTI mode is signaled(4101). If shortened-TTI mode is higher-layer signaled, the UE preparesto receive control and data signals in shortened-TTI mode (4103).

If normal-TTI mode is higher-layer signaled, the UE prepares to receivecontrol and data signals in normal-TTI mode (4105).

In this embodiment, when shortened-TTI mode is notified by the BS to theUE that is operating in normal-TTI mode to send and receive a control ordata signal, to allow the UE to operate again in normal-TTI mode,normal-TTI mode is to be notified by the BS to the UE through higherlayer signaling.

The transmission mode may be changed in various ways. For example, theBS and the UE can make an agreement in advance that when shortened-TTImode is higher-layer signaled at a first point in time, the transmissionmode returns to normal-TTI mode after a given time from the first pointin time. Here, higher layer signaling may carry information on theduration for shortened-TTI mode operation or information on the time forreturning to normal-TTI mode.

As such, the UE may operate in normal-TTI mode after the agreed timewithout separate higher layer signaling from the BS.

Thirteenth Embodiment

In the thirteenth embodiment, a description is given of the structure ofdownlink control and data signals used by the BS when the BS notifiesthe UE of transmission and reception in shortened-TTI mode throughhigher layer signaling with reference to FIG. 42 .

FIG. 42 illustrates resources in the overall downlink frequencybandwidth 4202 during one subframe 4204.

A single subframe 4204 may be divided into two slots 4206 and 4208. A UEhaving received a notification of shortened-TTI mode through higherlayer signaling may receive control and data signals in each slot.

In FIG. 42 , the downlink control signal channel (PDCCH) 4210 is mappedto up to the first three OFDM symbols of the first slot (4206). Thisregion carries PCFICH and PHICH information and may be used to mapcontrol signals for normal-TTI UEs. Control signals for shortened-TTIUEs may be mapped to the PDCCH 4210 or to the EPDCCH region 4212 insidethe slot.

The EPDCCH 4212 may indicate a downlink control signal mapped to an RBwithin a slot and may carry scheduling assignment information for a UE.The RB where the EPDCCH 4212 can be present may be higher-layer signaledto a shortened-TTI UE.

The UE identifies the location of the RB to which downlink data ismapped by use of a control signal mapped to the PDCCH 4210 or EPDCCH4212 and receives the PDSCH 4214 as data in the first slot of theidentified RB location. The BS may notify in advance a shortened-TTI UEof the OFDM symbol numbers corresponding respectively to the starts ofthe EPDCCH 4212 and the PDSCH 4214 through higher layer signaling.

Control signals may be mapped to the PDCCH 4210 only without use of theEPDCCH 4212.

In FIG. 42 , downlink control signals in the second slot may be mappedto up to the first three OFDM symbols of the second slot 4208, and thelocation or length of RBs 4218 in the second slot available toshortened-TTI UEs may be higher-layer signaled in advance.

In addition, a control signal may be carried by the EPDCCH region 4220that may be transmitted in the second slot of a specific RB, and the RBto which the EPDCCH region 4220 is mapped may be higher-layer signaledto a shortened-TTI UE in advance. Information on the second slot data(PDSCH 4224) is mapped to the PDCCH 4216 or EPDCCH 4220 in the secondslot.

Control signals may be mapped to the PDCCH 4216 only without use of theEPDCCH 4220.

The PDCCH 4216 to which downlink control signals can be mapped in thesecond slot may be utilized in the same manner as in the case of thefifth embodiment.

The EPDCCH regions 4212 and 4220 to which downlink control signals canbe mapped respectively in the first slot and in the second slot may beutilized in the same manner as in the case of the sixth or seventhembodiment.

In the existing LTE or LTE-A system, EREG 0 to EREG 15 are formed to mapthe EPDCCH to resource elements by numbering resource elements of aresource block in a frequency-first manner from 0 to 15. In this EREGnumbering, resource elements used to map DM-RS are excluded.

Meanwhile, in embodiments of the present invention depicted in FIG. 42or 43 , the EPDCCH used for shortened-TTI transmission is mapped onlywithin the slot. This mapping may be performed only within the slot byforming EREGs similarly to the case of the existing EDPCCH or by formingEREG 0 to EREG 7 (other than EREG 0 to EREG 15) in one resource block.Alternatively, the EPDCCH may be mapped to a resource block within oneslot similarly to the case of the existing PDCCH or similarly to thecase of the existing PDSCH.

EPDCCH resource mapping for shortened-TTI transmission described abovemay be modified in various ways. Hence, the EDPCCH in one subframe fornormal-TTI transmission and the EDPCCH in one slot for shortened-TTItransmission may be present in the same resource block or in differentresource blocks.

Meanwhile, the BS may notify in the second slot a shortened-TTI UE ofthe OFDM symbol numbers corresponding respectively to the starts of theEPDCCH 4216 and the PDSCH 4224 through higher layer signaling inadvance.

In the second slot, control signals may be mapped only to the EPDCCHregion 4220 without use of the PDCCH 4216 to which downlink controlsignals can be mapped.

FIG. 43 shows the EPDCCH region 4316 to which downlink control signalsare mapped in the second slot of a resource block and the PDSCH region4320 to which data is mapped in the second slot without use of the PDCCH4216 shown in FIG. 42 .

In FIG. 42 or 43 , the PDSCH region 4222 or 4322 for normal-TTI mode ismapped to a resource block in one subframe. The location or length of aresource block to which the PDSCH 4222 or 4322 for normal-TTI UEs ismapped may be higher-layer signaled to shortened-TTI UEs.

Fourteenth Embodiment

The fourteenth embodiment relates to a method where the UE sends the BSa HARQ ACK/NACK signal for the PDCCH and EPDCCH associated with PDSCH orSPS transmission when the BS operates the LTE or LTE-A system. Thefourteenth embodiment is described with reference to FIGS. 44, 45A, 45B,45C, 45D, 45E, 46A, 46B, 46C, 46D, 46E, and 47 . In the followingdrawings, “SF” denotes the slot number in one frame (10 ms).

First, a description is given of the LTE system supporting time-divisionduplex (TDD).

In the existing LTE or LTE-A TDD system, the UE sends the BS an ACK/NACKsignal at subframe n through an uplink channel for the PDCCH and EPDCCHassociated with PDSCH or SPS transmission sent at subframe n-k of thedownlink. Here, k is an element of a set K prepared according to the TDDconfiguration and subframe number.

In the fourteenth embodiment, the UE operating in shortened-TTI modesends the BS an ACK/NACK signal at slot n through an uplink channel forthe PDCCH and EPDCCH associated with PDSCH or SPS transmission sent inshortened-TTI mode at slot n-k of the downlink.

That is, while the point in time to send an uplink ACK/NACK signal isdetermined on a subframe basis in the related art, the point in time tosend an uplink ACK/NACK signal is determined on a slot basis in thefourteenth embodiment of the present invention. Hence, it is necessaryto redefine n and k of n-k (serving as a reference for sending an uplinkACK/NACK signal for PDCCH and EPDCCH) in terms of slot number within theLTE frame.

In this case, k is an element of a set K prepared according to the TDDconfiguration and slot number. An example for the set K is illustratedin FIG. 44 .

For example, for TDD configuration 0 and slot 4, the slot number n is 4.In this case, an ACK/NACK signal is sent for the PDCCH and EPDCCHassociated with PDSCH or SPS transmission received by the UE at slotn-k. Referring to the table of FIG. 44 , k=4. That is, for the PDCCH andEPDCCH associated with PDSCH or SPS transmission received by the UE atslot 0, an ACK/NACK signal is sent to the BS at slot 4.

As another example, for TDD configuration 5 and slot 5, the slot numbern is 5. In this case, referring to the table, the set K is given by {4,5, 6, 7, 8, 9, 10, 11}. Hence, ACK/NACK signals are sent to the BS atslot 5 for the PDCCH and EPDCCH associated with PDSCH or SPStransmission received by the UE at slot n-k (slot 1 and slot 0 ofcurrent frame, and slot 19, slot 18, slot 17, slot 16, slot 15 and slot14 of previous frame).

The table of FIG. 44 is merely an example and may be modified in variousways. In the TDD system, while the BS schedules a second type UE to usea specific subframe for the uplink, the BS may also schedule a firsttype UE to use the subframe for the downlink. In this case, the timingwhen the first type UE sends HARQ ACK/NACK feedback may be differentfrom that of the present embodiment.

For example, the HARQ ACK/NACK function performed using the table ofFIG. 44 may also be performed using the tables of FIGS. 45A, 45B, 45C,45D, 45E, 46A, 46B, 46C, 46D, and 46E.

Meanwhile, the configuration shown in different tables of FIGS. 33, 35,46A, 46B, 46C, 46D, and 46E may be not limited to only one table itself.For example, the HARQ ACK/NACK transmission scheme may be performed byusing a table created by combining different tables shown in FIGS. 33,35, 46A, 46B, 46C, 46D, and 46E.

FIG. 47 depicts a procedure for the UE operating in shortened-TTI modeto send HARQ ACK/NACK feedback to the BS in the LTE or LTE-A TDD system.

First, the UE identifies the TDD configuration and slot number n inoperation (4702). The UE may obtain information on the TDD configurationfrom the system information, and obtain information on the slot number nfrom the master information block and synchronization signals.

The UE determines whether an element exists in the set K correspondingto the TDD configuration and slot number at slot n (4704). If there isno element in the set K, as there is no HARQ ACK/NACK feedback to besent at slot n, the UE may prepare to receive a downlink signal for thenext slot (4708).

If there is an element in the set K, as there may be HARQ ACK/NACKfeedback to be sent at slot n, the UE sends, for each element k of theset K, the BS an ACK/NACK signal at slot n for the PDCCH and EPDCCHassociated with PDSCH or SPS transmission received at slot n-k (4706).

The set K may be found from the tables of FIGS. 44, 45A, 45B, 45C, 45D,45E, 46A, 46B, 46C, 46D, and 46E or from a new table created bycombining the existing tables.

In the above description, a scheme is proposed for sending ACK/NACKfeedback for the PDCCH and EPDCCH associated with PDSCH or SPStransmission received by the UE in the LTE TDD system.

On the other hand, for the LTE system operating in frequency divisionduplex (FDD) mode, the value of k of TDD mode may be fixed to 3, 4, 5,6, 7, or 8 for every slot. For example, when k=4 in the LTE FDD system,the UE sends an HARQ ACK/NACK signal at slot n for the PDCCH and EPDCCHassociated with PDSCH or SPS transmission received at slot n−4.

Fifteenth Embodiment

The fifteenth embodiment relates to a method where the BS operating theLTE or LTE-A system sends the UE a HARQ ACK/NACK signal for the uplinkdata channel PUSCH. The fifteenth embodiment is described with referenceto FIGS. 48, 49A, 49B, 49C, 49D, 49E, 50A, 50B, 50C, 50D, 50E, and 51 .In the following drawings, “SF” denotes the slot number in one frame (10ms).

In the existing LTE or LTE-A TDD system, the BS sends the UE an ACK/NACKsignal at subframe n+k through the PHICH for the PUSCH sent at subframen of the uplink. Here, k is an element of a set K prepared according tothe TDD configuration and subframe number.

In the fifteenth embodiment, the BS sends the UE operating inshortened-TTI mode an ACK/NACK signal at slot n+k through a downlinkchannel for the PUSCH sent at slot n of the uplink in shortened-TTImode.

That is, while the point in time to send a downlink ACK/NACK signal isdetermined on a subframe basis in the related art, the point in time tosend a downlink ACK/NACK signal is determined on a slot basis in thefifteenth embodiment of the present invention. Hence, it is necessary toredefine n and k of n+k (serving as a reference for sending a downlinkACK/NACK signal) in terms of slot number within the LTE frame.

In this case, k is an element of a set K determined in advance accordingto the TDD configuration and slot number. An example for the set K isillustrated in FIG. 48 .

For example, for TDD configuration 0 and slot 4, the slot number n is 4.In this case, the BS sends the UE a HARQ ACK/NACK signal at slot n+k forthe PUSCH sent by the UE at slot n. Referring to the table of FIG. 48 ,k=6. That is, for the PUSCH sent by the UE at slot 4, the BS sends theUE a HARQ ACK/NACK signal at slot 10 through a downlink channel.

As another example, for TDD configuration 5 and slot 5, the slot numbern is 5. In this case, referring to the table, the set K is given by {4}.That is, for the PUSCH sent by the UE at slot 5 (slot n), the BS sendsthe UE an ACK/NACK signal at slot 9 (slot n+k).

As further example, the BS may use the set K in the tables of FIGS. 49A,49B, 49C, 49D, 49E, 50A, 50B, 50C, 50D, and 50E to send the UE a HARQACK/NACK signal for the PUSCH.

Meanwhile, the configuration shown in different tables of FIGS. 48, 49A,49B, 49C, 49D, 49E, 50A, 50B, 50C, 50D, and 50E may be not limited toonly one table itself. For example, HARQ ACK/NACK transmission may beperformed by using a table created by combining different configurationsshown in the tables of FIGS. 48, 49A, 49B, 49C, 49D, 49E, 50A, 50B, 50C,50D, and 50E.

FIG. 51 is a flowchart depicting a procedure for the BS to send HARQACK/NACK feedback through a downlink channel to the UE operating inshortened-TTI mode in the LTE or LTE-A TDD system.

The BS identifies the TDD configuration and slot number n in operation(5101).

The BS determines whether a PUSCH transmission is scheduled at slot nfrom the UE (5103). If PUSCH data transmission is scheduled at slot n,the BS sends the UE a corresponding HARQ ACK/NACK signal at slot n+kthrough a downlink channel (4905). The set K may be found from thetables of FIGS. 48, 49A, 49B, 49C, 49D, 49E, 50A, 50B, 50C, 50D, and 50Eor from a new table created by combining configurations given in theabove tables.

If PUSCH data transmission is not scheduled at slot n, as there is noHARQ ACK/NACK signal to be sent to the UE at slot n, the BS prepares fornext-slot operation (5107).

In the above description, a scheme is proposed for sending ACK/NACKfeedback in a TDD system. In the existing LTE TDD system, the BS and theUE can make an agreement in advance that shortened-TTI transmission doesnot occur at the special subframe.

In the above description, a scheme is proposed that enables the BS tosend the UE a HARQ ACK/NACK signal for the PUSCH in the LTE TDD system.For the LTE system operating in frequency division duplex (FDD) mode,the value of k of TDD mode may be fixed to 3, 4, 5, 6, 7, or 8 for everyslot. For example, when k=4 in the LTE FDD system, the BS sends the UEan HARQ ACK/NACK signal at slot n+4 through the PHICH or anotherdownlink control channel for the PUSCH received by the BS at slot n.

Sixteenth Embodiment

The sixteenth embodiment relates to a method for calculating thetransport block size (TBS) indicating the number of information bitscontained in one codeword when the BS and the UE send data. Thesixteenth embodiment is described with reference to FIGS. 52, 53A, and53B.

FIG. 52 shows a table used for determining the TBS index based on theMCS index in the existing LTE system.

For example, in the table of FIG. 52 , when the MCS index is 10, thecorresponding TBS index is 9.

FIGS. 53A and 53B show tables used for determining the TBS according tothe number of PRBs allocated to the UE and the TBS index in the existingLTE system.

For example, when the number of PRBs allocated to a UE is 25 and the MCSindex is 9, the TBS is 4008.

As the tables of FIGS. 53A and 53B illustrate TBS computation whentransmission is carried out on a subframe basis, it is necessary tonewly define a scheme for TBS computation when transmission is carriedout in shortened-TTI mode. When a short TTI shorter than one subframesuch as a slot, 2 OFDM symbols or 1 OFDM symbol is employed, the valuecorresponding to the number of PRBs is newly computed using Equation 9below and used to determine the TBS.N _(PB)=max{└N _(PRB)′×α┘,1}  [Equation 9]

In Equation 9, N_(PRB)′ indicates the number of PRBs actually allocatedto the UE, and N_(PRB) is the result of this computation and is used tofind the TBS, for example, in the table of FIGS. 53A and 53B.

In Equation 9, max{a,b} returns the largest value among a and b. └a┘returns the greatest integer less than or equal to a. In the aboveequation, └a┘ may be replaced by ┌a┐, where ┌a┐ returns the leastinteger greater than or equal to a. In Equation 9, α can be selected asa real number greater than 0 and less than 1. For example, in the caseof shortened-TTI mode with a 0.5 ms TTI, α can be set to 0.3, 0.4 or4/14 for the first slot in TBS determination and can be set to 0.7, 0.6or 7/14 for the second slot. The TBS determined in this way may be usedby the UE and the BS as the number of information bits contained in onecodeword. When a first type UE uses a TTI less than 0.5 ms, it may set αto a different value for TBS determination. In addition, whentransmission is carried out to first type UEs using different-lengthTTIs, or when transmission is carried out to a first type UEs usingdifferent-length TTIs, α may be set to a different value according tothe TTI length.

Equation 9 used for TBS determination in the sixteenth embodiment doesnot need to be limited to shortened-TTI mode using a 0.5 ms slot as theTTI unit. Equation 9 may also be applied to shortened-TTI mode usingvarious lengths like one OFDM symbol and two OFDM symbols as the TTIunit.

In the above embodiments of the present invention, a shortened-TTI UEindicates a UE supporting shortened-TTI transmission. A shortened-TTI UEmay also support normal-TTI transmission, and in this case it transmitsdownlink and uplink control information in the same way as a normal-TTIUE.

To carry out the above embodiments of the present invention, FIGS. 38and 39 show a user equipment and a base station each including atransmitter, a receiver, and a processor. Operations of the BS and theUE for transmitting shortened-TTI downlink control signals are describedin the first to seventh embodiments. To carry out these operations, thetransmitters, receivers and processors of the BS and the UE shouldfunction according to each of the above embodiments. Operations of theBS and the UE for transmitting shortened-TTI uplink control signals aredescribed in the eighth and ninth embodiments. To carry out theseoperations, the transmitters, receivers and processors of the BS and theUE should function according to each of the above embodiments.

Specifically, FIG. 38 is a block diagram showing the internal structureof a user equipment according to an embodiment of the present invention.As shown in FIG. 38 , the UE may include a terminal receiver 3800, aterminal transmitter 3804, and a terminal processor 3802.

In one embodiment, the terminal receiver 3800 and the terminaltransmitter 3804 may be collectively referred to as a transceiver. Thetransceiver may send and receive a signal to and from a base station.The signal may include control information, and data.

To this end, the transceiver may include a radio frequency (RF)transmitter for upconverting the frequency of a signal to be transmittedand amplifying the signal, and an RF receiver for low-noise amplifying areceived signal and downconverting the frequency of the received signal.The transceiver may receive a signal through a radio channel and outputthe received signal to the terminal processor 3802, and may send asignal from the terminal processor 3802 through a radio channel.

The terminal processor 3802 may control a series of operations so thatthe UE can function according to the above embodiments of the presentinvention.

FIG. 39 is a block diagram showing the internal structure of a basestation according to an embodiment of the present invention. As shown inFIG. 39 , the BS may include a BS receiver 3900, a BS transmitter 3904,and a BS processor 3902.

In one embodiment, the BS receiver 3900 and the BS transmitter 3904 maybe collectively referred to as a transceiver. The transceiver may sendand receive a signal to and from a user equipment. The signal mayinclude control information, and data.

To this end, the transceiver may include an RF transmitter forupconverting the frequency of a signal to be transmitted and amplifyingthe signal, and an RF receiver for low-noise amplifying a receivedsignal and downconverting the frequency of the received signal. Thetransceiver may receive a signal through a radio channel and output thereceived signal to the BS processor 3902, and may send a signal from theBS processor 3902 through a radio channel.

The BS processor 3902 may control a series of operations so that the BScan function according to the above embodiments of the presentinvention.

For example, the BS processor 3902 may determine whether a UE to bescheduled is a first type UE or a second type UE, and, if the UE to bescheduled is a first type UE, control an operation to generate controlinformation on the basis of control information for the first type UE.In this case, the TTI length for the first type UE may be shorter thanthat for the second type UE.

In one embodiment of the present invention, the BS processor 3902 maycontrol an operation to generate downlink control information (DCI) forthe first type UE. In this case, the DCI may indicate controlinformation for the first type UE.

In one embodiment of the present invention, the BS processor 3902 maycontrol an operation to generate the DCI for the first type UE on thebasis of a UE identifier for the first type UE. In one embodiment of thepresent invention, the BS processor 3902 may control an operation to mapthe DCI for the first type UE to a search space for the first type UE.

In one embodiment of the present invention, the BS processor 3902 maycontrol an operation to generate downlink control information (DCI)including resource allocation information of a data channel for thefirst type UE.

In one embodiment of the present invention, the BS processor 3902 maycontrol an operation to send the UE, in the second slot of a subframe,information on the number of resource blocks to which a control signalfor the first type UE can be mapped or on a set of numbers each denotingthe number of resource blocks, and to send, in the second slot of thesubframe, the DCI for the first type UE on the basis of the aboveinformation.

In one embodiment of the present invention, the BS processor 3902 maycontrol an operation to generate enhanced control information for thefirst type UE. The enhanced control information may be mapped, in thefirst slot of a subframe, to the remaining symbols of the first slotexcept for pre-designated symbols, and be mapped, in the second slot ofthe subframe, to the remaining symbols of the second slot except forpre-designated symbols.

In one embodiment of the present invention, the BS processor 3902 maycontrol an operation to map the enhanced control information for thefirst type UE to a resource block to which enhanced control informationfor the first type UE can be mapped.

In one embodiment of the present invention, the BS processor 3902 maycontrol a process of determining the number of resource blocks availableto the uplink control information (UCI) format for a first type UE andsending information on the determination result, allocating resourcesfor a first type UE to each UE without exceeding the determined numberof resource blocks and sending information on the allocation result, andsending control information and data associated with the controlinformation according to the resources allocated to each UE.

Hereinabove, various embodiments of the present invention have beenshown and described for the purpose of illustration without limiting thesubject matter of the present invention. It should be understood thatmany variations and modifications of the basic inventive conceptdescribed herein will still fall within the spirit and scope of thepresent invention as defined in the appended claims and theirequivalents. In addition, it is possible to combine the individualembodiments if necessary for joint operation. For example, the thirdembodiment and the seventh embodiment of the present invention can becombined for operations of the base station and user equipment.

What is claimed is:
 1. A method performed by a base station in awireless communication system, the method comprising: transmitting, to aterminal, configurations for a plurality of physical uplink controlchannel (PUCCH) resources; transmitting, to the terminal, downlinkcontrol information (DCI) on a physical downlink control channel(PDCCH), wherein the DCI includes a resource indicator for indicating aPUCCH resource among the plurality of PUCCH resources; and receiving,from the terminal, uplink control information (UCI) on the PUCCHresource indicated by the resource indicator, wherein a configurationfor a PUCCH resource comprises information on a resource bloc k (RB) andinformation on a number of symbols.
 2. The method of claim 1, furthercomprising: transmitting, to the terminal, information for configuring aplurality of control resource sets, wherein the PDCCH is transmitted ina control resource set among the plurality of control resource sets. 3.The method of claim 2, wherein: the information for configuring theplurality of control resource sets includes information on each controlresource set comprising information on resource blocks (RBs) allocatedto each control resource set and information on a duration associatedwith each control resource set, and the duration is one of 1, 2, or 3symbols.
 4. The method of claim 1, wherein a frequency hopping isapplied for the PUCCH resource.
 5. A method performed by a terminal in awireless communication system, the method comprising: receiving,configurations for a plurality of physical uplink control channel(PUCCH) resources; receiving, from the base station, downlink controlinformation (DCI) on a physical downlink control channel (PDCCH),wherein the DCI includes a resource indicator for indicating a PUCCHresource among the plurality of PUCCH resources; and transmitting, tothe base station, uplink control information (UCI) on the PUCCH resourceindicated by the resource indicator, wherein a configuration for a PUCCHresource comprises information on a resource block (RB) and informationon a number of symbols.
 6. The method of claim 5, further comprising:receiving, from the base station, information for configuring aplurality of control resource sets, wherein the PDCCH is received in acontrol resource set among the plurality of control resource sets. 7.The method of claim 6, wherein: the information for configuring theplurality of control resource sets includes information on each controlresource set comprising information on resource blocks (RBs) allocatedto each control resource set and information on a duration associatedwith each control resource set, and the duration is one of 1, 2, or 3symbols.
 8. The method of claim 5, wherein a frequency hopping isapplied for the PUCCH resource.
 9. A base station in a wirelesscommunication system, the base station comprising: a transceiver; and acontroller coupled with the transceiver and configured to control to:transmit, to a terminal, configurations for a plurality of physicaluplink control channel (PUCCH) resources; transmit, to the terminal,downlink control information (DCI) on a physical downlink controlchannel (PDCCH), wherein the DCI includes a resource indicator forindicating a PUCCH resource among the plurality of PUCCH resources; andreceive, from the terminal, uplink control information (UCI) on thePUCCH resource indicated by the resource indicator, wherein aconfiguration for a PUCCH resource comprises information on a resourceblock (RB) and information on a number of symbols.
 10. The base stationof claim 9, wherein the controller is further configured to: transmit,to the terminal, information for configuring a plurality of controlresource sets, wherein the PDCCH is transmitted in a control resourceset among the plurality of control resource sets.
 11. The base stationof claim 10, wherein: the information for configuring the plurality ofcontrol resource sets includes information on each control resource setcomprising information on resource blocks (RBs) allocated to eachcontrol resource set and information on a duration associated with eachcontrol resource set, and the duration is one of 1, 2, or 3 symbols. 12.The base station of claim 9, wherein: a frequency hopping is applied forthe PUCCH resource, and at least one modulated symbol for the UCI isprocessed based on a block-wise spreading, a discrete fourier transform(DFT), an inverse fast fourier transform (IFFT).
 13. A terminal in awireless communication system, the terminal comprising: a transceiver;and a controller coupled with the transceiver and configured to controlto: receive, from a base station, configurations for a plurality ofphysical uplink control channel (PUCCH) resources; receive, from thebase station, downlink control information (DCI) on a physical downlinkcontrol channel (PDCCH), wherein the DCI includes a resource indicatorfor indicating a PUCCH resource among the plurality of PUCCH resources;and transmit, to the base station, uplink control information (UCI) onthe PUCCH resource indicated by the resource indicator, wherein aconfiguration for a PUCCH resource comprises information on a resourceblock (RB) and information on a number of symbols.
 14. The terminal ofclaim 13, wherein the controller is further configured to: receive, fromthe base station, information for configuring a plurality of controlresource sets, wherein the PDCCH is received in a control resource setamong the plurality of control resource sets.
 15. The terminal of claim14, wherein: the information for configuring the plurality of controlresource sets includes information on each control resource setcomprising information on resource blocks (RBs) allocated to eachcontrol resource set and information on a duration associated with eachcontrol resource set, and the duration is one of 1, 2, or 3 symbols. 16.The terminal of claim 13, wherein: a frequency hopping is applied forthe PUCCH resource, and at least one modulated symbol for the UCI isprocessed based on a block-wise spreading, a discrete fourier transform(DFT), an inverse fast fourier transform (IFFT).